Patent Publication Number: US-11392084-B2

Title: Image forming apparatus to which cartridge is attachable and including controller capable of determining whether cartridge is attached to image forming apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2019-178765 filed Sep. 30, 2019. The entire content of the priority application is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to an image forming apparatus. 
     BACKGROUND 
     An electro-photographic type image forming apparatus such as a laser printer and an LED printer is well known in the art. The image forming apparatus includes a drum cartridge and a toner cartridge. The drum cartridge includes a photosensitive drum. The toner cartridge includes a developing roller. The toner cartridge is attachable to and detachable from the drum cartridge. In a case where the toner cartridge is attached to the drum cartridge, the developing roller of the toner cartridge and the photosensitive drum of the drum cartridge are in contact with each other. 
     Further, there has been conventionally known a toner cartridge including a toner memory serving as a storage medium. The toner memory stores various information with respect to the toner cartridge. In recent years, the image forming apparatus handles not only information related to the toner cartridge, but also information related to the drum cartridge. Therefore, the drum cartridge is required to be provided with a drum memory serving as a storage medium for storing information related to the drum cartridge. 
     SUMMARY 
     There is such a conventional image forming apparatus that has both of a drum memory and a toner memory. In the conventional image forming apparatus, after a cover of the image forming apparatus is closed, a controller of the image forming apparatus determines whether communication with the drum memory is available. When the drum cartridge is not attached to the image forming apparatus, the controller determines that communication with the drum memory is not available. However, in the conventional image forming apparatus, when communication with the drum memory is not available, it cannot be determined whether the communication with the drum memory is not available because the drum cartridge is not attached to the image forming apparatus or because communication between the controller and the drum memory is disabled. 
     In view of the foregoing, it is an object of the present disclosure to provide a technology allowing determination of whether a cartridge is attached to an image forming apparatus and is established, without communication with the memory. 
     In order to attain the above and other objects, according to one aspect, the disclosure provides an image forming apparatus including a controller, a main body frame, a cartridge and a display. The cartridge is attachable to the main body frame. The cartridge includes a memory, a cartridge data terminal and a cartridge detection terminal. The memory stores information related to the cartridge. The cartridge data terminal is configured to communicate the information stored in the memory. The controller includes a main body data terminal and a main body detection terminal. The main body data terminal is electrically connected to the cartridge data terminal in a case where the cartridge is attached to the main body frame. The main body detection terminal is electrically connected to the cartridge detection terminal in the case where the cartridge is attached to the main body frame. The controller is configured to perform determining whether the main body detection terminal and the cartridge detection terminal are electrically connected with each other. The controller is configured to perform displaying a determination result of the determining whether the main body detection terminal and the cartridge detection terminal are electrically connected with each other on the display. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The particular features and advantages of the disclosure will become apparent from the following description taken in connection with the accompanying drawings, in which: 
         FIG. 1  is a conceptual diagram illustrating an image forming apparatus according to one embodiment of the present disclosure; 
         FIG. 2  is a perspective view illustrating a drum cartridge according to the embodiment; 
         FIG. 3  is another perspective view illustrating the drum cartridge according to the embodiment; 
         FIG. 4  is a perspective view illustrating a first connector, a plurality of second connectors, a drum circuit board, and harnesses according to the embodiment; 
         FIG. 5  is a perspective view illustrating a toner cartridge according to the embodiment; 
         FIG. 6  is a block diagram showing an electrical connection among a controller, the drum circuit board, and four toner memories according to the embodiment; 
         FIG. 7  is a flowchart illustrating a process for determining whether the drum cartridge is attached to the image forming apparatus; 
         FIG. 8  is a flowchart illustrating a process for determining whether the toner cartridge is attached to the drum cartridge; 
         FIG. 9  is a block diagram showing an electrical connection among the controller, the drum circuit board, and the toner memory according to a first modification; 
         FIG. 10  is a block diagram showing an electrical connection among the controller, the drum circuit board, and the toner memory according to a second modification; 
         FIG. 11  is a block diagram showing an electrical connection among the controller, the drum circuit board, and the toner memory according to a third modification; and 
         FIG. 12  is a block diagram showing an electrical connection among the controller, the drum circuit board, and the toner memory according to a fourth modification. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an image forming apparatus  100  according to one embodiment of the present disclosure will be described with reference to  FIGS. 1 through 8 . 
     In the following description, an extending direction of a photosensitive drum will be referred to as a “first direction”. Further, a direction in which a plurality of photosensitive drums are arranged will be referred to as a “second direction”. The first direction and the second direction intersect with each other. Preferably, the first direction and the second direction are perpendicular to each other. 
     &lt;1. Configuration of Image Forming Apparatus&gt; 
       FIG. 1  is a conceptual diagram of the image forming apparatus  100 . The image forming apparatus  100  is an electro-photographic printer. The image forming apparatus  100  may be a laser printer or a light emitting diode (LED) printer, for example. As illustrated in  FIG. 1 , the image forming apparatus  100  includes a main body frame  101 , a controller  102 , a display  103 , a cover  108 , a drum cartridge  1 , and a plurality of toner cartridges  2 . 
     The main body frame  1  has an insertion opening  101   a . The cover  8  is pivotally movable with respect to the main body frame  101  between a closed position and an open position. The closed position is a position where the cover  108  closes the insertion opening  101   a , and the open position is a position where the cover  108  opens the insertion opening  101   a . The image forming apparatus  100  includes a sensor  109 . The sensor  109  is configured to detect whether the cover  108  is pivoted from the open position to the closed position. When the sensor  109  detects that the cover  108  has pivoted from the open position to the closed position, a detection signal indicating that the cover has pivoted to the closed position is sent to the controller  102 . 
     Each of the plurality of toner cartridges  2  can be individually attached to the drum cartridge  1 . The drum cartridge  1 , to which the plurality of the toner cartridges  2 , are attached can be attached to the main body frame  101  through the insertion opening  101   a . The plurality of toner cartridges  2  store toner (developing agents) of respective colors such as cyan, magenta, yellow, and black, respectively. The image forming apparatus  100  is configured to form an image on a recording surface of a printing sheet with toner supplied from the plurality of toner cartridges  2 . Although the number of the toner cartridges  2  attachable to the drum cartridge  1  is four according to this embodiment, the number of toner cartridges  2  attachable to the drum cartridge  1  may be one, two, three, five or more. 
     The drum cartridge  1  includes a drum circuit board  15  and a drum memory  151 . The drum memory  151  is a storage medium, to which information can be written and from which information can be read. Each of the plurality of toner cartridges  2  includes a toner memory  24 . The toner memory  24  is a storage medium, to which information can be written and from which information can be read. 
     The controller  102  is positioned inside the main body frame  101  of the image forming apparatus  100 . The controller  102  includes, for example, a circuit board, a processor  105  such as a CPU, and a main body memory  106  serving as a storage medium. The controller  102  executes various processes by the processor  105  operating according to a program stored in the main body memory  106 . Specifically, the controller  102  executes a reading process to read information from the main body memory  106  and an operating process for operating the image forming apparatus  100  based on the information read by the reading process. 
     In a case where the plurality of toner cartridges  2  are attached to the drum cartridge  1 , the toner memory  24  of each toner cartridge  2  is electrically connected to the drum circuit board  15 . Further, in a case where the drum cartridge  1  attached with the toner cartridges  2  is mounted in the main body frame  101 , the controller  102  in the main body frame  101  and the drum circuit board  15  are electrically connected with each other. Accordingly, the toner memory  24  of each of plurality of toner cartridges  2  and the controller  102  are electrically connected with each other through the drum circuit board  15 . 
     The display  103  is, for example, a liquid crystal display or an organic EL display. The display  103  is configured to display various information with respect to the operation of the image forming apparatus  100  on a screen according to an instruction from the controller  102 . 
     &lt;2. Configuration of Drum Cartridge&gt; 
     Next, the configuration of drum cartridge  1  will be described.  FIGS. 2 and 3  are perspective views of the drum cartridge  1 . 
     As illustrated in  FIGS. 2 and 3 , the drum cartridge  1  includes a plurality of photosensitive drums  11 , a drum frame  12 , a first connector  13 , a plurality of second connectors  14  and the drum circuit board  15 . In the present embodiment, the number of the photosensitive drums  11  is four, and the number of the plurality of second connectors  14  is four. 
     Each of the photosensitive drums  11  is configured to transfer toner supplied from the toner cartridge  2  to printing paper. The plurality of photosensitive drums  11  are arranged in the second direction at predetermined intervals therebetween. Each of the photosensitive drums  11  has a cylindrical outer peripheral surface extending in the first direction. The outer peripheral surface of the photosensitive drum  11  is covered with a photosensitive material. Further, each of the photosensitive drums  11  is rotatable about a rotation axis extending in the first direction. 
     The drum frame  12  is a frame body for holding the plurality of photosensitive drums  11 . The drum frame  12  includes a plurality of toner cartridge holders  121 . The plurality of toner cartridge holders  121  are arranged in the second direction at predetermined intervals therebetween. Each of the toner cartridge  2  is attachable to the corresponding toner cartridge holder  121 . Thus, the plurality of the toner cartridges are attachable to the drum frame  12 . When one of the toner cartridges  2  is attached to the toner cartridge holder  121 , the outer peripheral surface of the photosensitive drum  11  and an outer peripheral surface of the developing roller  22  provided in the toner cartridge  2  (described later) are in contact with each other. 
       FIG. 4  is a perspective view illustrating the first connector  13 , the plurality of the second connectors  14 , the drum circuit board  15  and harnesses  16  and  17  for connecting the first connector  13 , the plurality of second connectors  14  and the drum circuit board  15 . 
     The first connector  13  is for being electrically connected to one or more terminals provided at the main body frame  101  when the drum cartridge  1  is attached to the main body frame  101  of the image forming apparatus  100 . The first connector  13  is, for example, fixed to a surface of the drum frame  12 . Incidentally, the first connector  13  may be immovable or slightly movable with respect to the drum frame  12 . The first connector  13  has a plurality of first terminals  131 . Each of the first terminals  131  is a conductor exposed on a surface of the drum frame  12 . Each of the first terminals  131  is electrically connected to a corresponding one of a plurality of main body side drum voltage terminals  31  (described later) of the drum circuit board  15 . 
     The plurality of second connectors  14  are for being electrically connected to terminals  242  of the toner memories  24  (described later) when the toner cartridges  2  are attached to the toner cartridge holders  121 . The plurality of second connectors  14  are provided for the toner cartridge holders  121 , respectively. Each of the second connectors  14  is located at an end of the corresponding toner cartridge holder  121  in the first direction. Further, each of the plurality of second connectors  14  is, for example, fixed to the surface of the drum frame  12 . Incidentally, the plurality of second connector  14  may be immovable or slightly movable with respect to the drum frame  12 . Each of the plurality of second connectors  14  has a plurality of second terminals  141 . Each of the second terminals  141  is a conductor exposed on the surface of the drum frame  12 . Each of the second terminals  141  is electrically connected to a corresponding one of a plurality of toner side drum voltage terminals  32  (described later) of the drum circuit board  15 . 
     The drum circuit board  15  is a circuit board electrically connected to the first connector  13  and the plurality of second connectors  14 . The drum circuit board  15  is, for example, fixed to the surface of the drum frame  12 . As illustrated in  FIG. 4 , the drum circuit board  15  is electrically connected with the first connector  13  through the first harness  16 . Further, the drum circuit board  15  is electrically connected with the plurality of second connectors  14  through the second harness  17 . Each of the first harness  16  and the second harness  17  is a wire harnesses including a plurality of conducting wires, for example. 
     Further, as illustrated in  FIG. 4 , the drum cartridge  1  includes the drum memory  151  serving as a storage medium. The drum memory  151  is provided on the drum circuit board  15 . Incidentally, the drum memory  151  may not be provided on the drum circuit board  15 . Specifically, the drum memory  151  may be provided at a surface of the drum frame  12 . 
     The drum memory  151  stores therein various information related to the drum cartridge  1 . For example, the drum memory  151  stores therein at least one of information identifying the drum cartridge  1  and information indicating the characteristics of the drum cartridge  1 . The information identifying the drum cartridge  1  includes, for example, at least one of: a manufacturing serial number of the drum cartridge  1 ; and an identification code indicating that the drum cartridge  1  is a genuine product. The information indicating the characteristics of the drum cartridge  1  includes, for example, at least one of the following pieces of information: information indicating models of image forming apparatuses to which the drum cartridge  1  is attachable; a specification of the drum cartridge  1 ; a service life of the photosensitive drum  11 ; charging characteristics of the photosensitive drum  11 ; information indicating whether the drum cartridge  1  is new; the total number of rotations by which the photosensitive drum  11  has been rotated; the total length of the charged times during which the photosensitive drum  11  has been charged; the total number of sheets that have been printed by the photosensitive drum  11 ; and an error history of the drum cartridge  1 . 
     The drum memory  151  has a first storage area and a second storage area. The first storage area is an area for storing non-rewritable information. The second storage area is an area for storing rewritable information. The first storage area stores therein, for example, at least one of: the manufacturing serial number; the identification code; the information indicating models of image forming apparatuses to which the drum cartridge  1  is attachable; the specification; and the service life of the photosensitive drum  11 , all of which is described above. The second storage area stores therein, for example, information indicating usage status of the drum cartridge  1 . The information indicating the usage status of the drum cartridge  1  includes, for example, at least one of: the information indicating whether the drum cartridge  1  is new; the total number of rotations by which the photosensitive drum  11  has been rotated; the total length of charged times during which the photosensitive drum  11  has been charged; the total number of sheets that have been printed by the photosensitive drum  11 ; and the error history of the drum cartridge  1 , all of which is described above. 
     &lt;3. Configuration of Toner Cartridge&gt; 
     Next, the configuration of the toner cartridge  2  will be described. In the following, the configuration of the toner cartridge  2  in the state where the toner cartridge  2  is attached to the drum cartridge  1  will be described using the above-described first direction and second direction. 
       FIG. 5  is a perspective view of the toner cartridge  2 . As illustrated in  FIG. 5 , the toner cartridge  2  includes a casing  21 , a developing roller  22 , a plurality of gears, a coupling  231 , a gear cover  232 , the toner memory  24 , and a holder  25 . 
     The casing  21  is a housing configured to accommodate toner therein. The casing  21  extends in the first direction between a first outer surface  211  and a second outer surface  212 . A chamber  213  is formed inside the casing  21 . The chamber  213  stores the toner therein. Further, the casing  2  has an opening  214 . The opening  214  is positioned at one end of the casing  21  in a third direction which intersects both of the first direction and the second direction. The chamber  213  communicates with an outside of the casing  21  through the opening  214 . 
     The developing roller  22  is a roller rotatable about a rotation axis extending in the first direction. The developing roller  22  is positioned at the opening  214  of the casing  21 . That is, the developing roller  22  is positioned at one end of the casing  21  in the third direction. When the toner cartridge  2  is attached to the drum cartridge  1 , the outer peripheral surface of the developing roller  22  is in contact with the outer peripheral surface of the photosensitive drum  11 . 
     The toner is supplied from the chamber  213  to the photosensitive drum  11  through the developing roller  22 . The toner carried on the outer surface of the developing roller  22  moves from the developing roller  22  to the photosensitive drum  11  according to the electrostatic latent image formed on the outer surface of the photosensitive drum  11 . As a result, the electrostatic latent image is developed into a visible image on the outer surface of the photosensitive drum  11 . 
     The plurality of gears, the coupling  231  and the gear cover  232  are positioned at the first outer surface  211  of the casing  21 . The gear cover  232  is fixed to the first outer surface  211  of the casing  21  with, for example, screws. At least one of the plurality of gears is positioned between the first outer surface  211  of the casing  21  and the gear cover  232 . The coupling  231  is exposed outside of the gear cover  232 . When the drum cartridge  1  attached with the toner cartridges  2  is attached to the main body frame  101  of the image forming apparatus  100 , drive shafts of the image forming apparatus  100  are connected to the couplings  231  of the toner cartridges  2 , and rotation of each drive shaft is transmitted to the developing roller  22  of the corresponding toner cartridge  2  through the coupling  231  and the plurality of gears of the corresponding toner cartridge  2 . 
     The toner memory  24  and the holder  25  are positioned between the first outer surface  211  of the casing  21  and the gear cover  232  in the first direction. The holder  25  holds the toner memory  24 . The holder  25  is movable relative to both of the casing  21  and the gear cover  232  in the second direction. Incidentally, the holder  25  may be fixed relative to both of the casing  21  and the gear cover  232 . Further, the toner memory  24  may be positioned at another position different from the position between the first outer surface  211  and the gear cover  232 . For example, the toner memory  24  may be positioned on a surface of the casing  21 . 
     The toner memory  24  has a plurality of terminals  242 . Each of the terminals  242  is a conductor exposed on a surface of the toner memory  24 . When the toner cartridge  2  is attached to the toner cartridge holder  121  of the drum cartridge  1 , the terminals  242  of the toner memory  24  are in contact with the second terminals  141  of the plurality of second connector  14 . In the present embodiment, the number of the terminals  242  of the toner memory  24  is four, and the number of the second terminals  141  of each second connector  14  is four. 
     The toner memory  24  stores therein various information related to the toner cartridge  2 . For example, the toner memory  24  stores therein at least one of information identifying the toner cartridge  2  and information indicating the characteristics of the toner cartridge  2 . The information identifying the toner cartridge  2  includes, for example, at least one of: a manufacturing serial number of the toner cartridge  2 ; and an identification code indicating that the toner cartridge is a genuine product. The information indicating the characteristics of the toner cartridge  2  includes, for example, at least one of the following pieces of information: information indicating models of image forming apparatuses to which the toner cartridge  2  can be used; a specification of the toner cartridge  2 ; a service life of the developing roller  22 ; information indicating whether the toner cartridge  2  is new; the total number of rotations by which the developing roller  22  has been rotated; the total number of sheets that have been printed by the developing roller  22 ; and an error history of the toner cartridge  2 . 
     &lt;4. Controller&gt; 
     Next, description will be made with respect to the terminals of the controller  102 .  FIG. 6  is a block diagram illustrating electrical connection between the controller  102 , the drum circuit board  15 , and the toner memories  24 . As illustrated in  FIG. 6 , the controller  102  has a plurality of main body terminals  104 . The plurality of main body terminals  104  include a main body voltage terminal  104   v , a main body ground terminal  104   g , a main body data terminal  104   d , a main body clock terminal  104   c , a main body detection terminal  104   s , and a main body interrupt terminal  104   i.    
     The main body voltage terminal  104   v  is a terminal for supplying voltage to a main body side drum voltage terminal  31   v  (described later) of the drum circuit board  15 . The controller  102  supplies a constant first voltage to the main body voltage terminal  104   v  based on power supplied from an outside of the controller  102 . 
     The main body ground terminal  104   g  is a terminal for grounding a main body side drum ground terminal  31   g  (described later) of the drum circuit board  15 . The voltage value of the main body ground terminal  104   g  is a constant ground voltage lower than the first voltage. 
     The main body data terminal  104   d  is a terminal for transmitting and receiving data between the controller  102  and the drum circuit board  15 . The main body data terminal  104   d  is electrically connected to the processor  105  of the controller  102 . 
     The main body clock terminal  104   c  is a terminal for supplying a clock signal having a constant period from the controller  102  to the drum circuit board  15 . 
     The main body detection terminal  104   s  is a terminal for detecting whether the drum cartridge  1  is attached to the main body frame  101 . As illustrated in  FIG. 6 , the controller  102  has a voltage measurement circuit  102   a  for measuring voltage at the main body detection terminal  104   s . Further, the controller  102  has a main body resistor  107 . The main body resistor  107  is an electric resistor. The main body resistor  107  has one end connected to the main body detection terminal  104   s  and another end connected to the main body voltage terminal  104   v.    
     The main body interrupt terminal  104   i  is a terminal for receiving an interrupt signal from a multiplexer  34  (described later). As illustrated in  FIG. 6 , the controller  102  has a signal detection circuit  102   b  for detecting the interrupt signal through the main body interrupt terminal  104   i  when the main body interrupt terminal  104   i  receives the interrupt signal from the multiplexer  34 . 
     &lt;5. Drum Circuit Board&gt; 
     The following describes in detail the configuration of the drum circuit board  15 . In the example of  FIG. 6 , the drum circuit board  15  has a plurality of main body side drum terminals  31 , a plurality of toner side drum terminals  32 , the multiplexer  34 , and a drum memory  151 . It should be noted that, as described above, the drum memory  151  may not be positioned on the drum circuit board  15 . Similarly, the multiplexer  34  may not be positioned on the drum circuit board  15 . For example, the multiplexer  34  and the drum memory  151  may be positioned on the surface of the drum frame  12 . 
     &lt;5-1. Main Body Side Drum Terminal&gt; 
     The plurality of main body side drum terminals  31  are electrically connected to the main body terminals  104  of the controller  102  through the above-described first connector  13  in the state where the drum cartridge  1  is attached to the main body frame  101  of the image forming apparatus  100 . This allows the drum circuit board  15  and the controller  102  to be electrically connected with each other. The plurality of main body side drum terminals  31  include a main body side drum voltage terminal  31   v , a main body side drum ground terminal  31   g , a main body side drum data terminal  31   d , a main body side drum clock terminal  31   c , a drum detection terminal  31   s , and a drum interrupt terminal  31   i.    
     The main body side drum voltage terminal (cartridge voltage terminal)  31   v  is electrically connected to the main body voltage terminal  104   v  in the state where the drum cartridge  1  is attached to the main body frame  101  of the image forming apparatus  100 . This allows the first voltage to be supplied from the controller  102  to the main body side drum voltage terminal  31   v  through the main body voltage terminal  104   v . As illustrated in  FIG. 6 , the main body side drum voltage terminal  31   v  is electrically connected to the drum memory  151 . 
     The main body side drum ground terminal (cartridge ground terminal)  31   g  is electrically connected to the main body ground terminal  104   g  in the state where the drum cartridge  1  is attached to the main body frame  101  of the image forming apparatus  100 . This allows the main body side drum ground terminal  31   g  to be grounded. That is, the voltage value of the main body side drum ground terminal  31   g  is the ground voltage lower than the first voltage. As illustrated in  FIG. 6 , the main body side drum ground terminal  31   g  is electrically connected to the drum memory  151 . 
     The main body side drum data terminal (cartridge data terminal)  31   d  is electrically connected to the main body data terminal  104   d  in the state where the drum cartridge  1  is attached to the main body frame  101  of the image forming apparatus  100 . This allows data to be transmitted and received between the controller  102  and the drum circuit board  15 . As illustrated in  FIG. 6 , the main body side drum data terminal  31   d  is electrically connected to the multiplexer  34  and the drum memory  151 . 
     The main body side drum clock terminal  31   c  is electrically connected to the main body clock terminal  104   c  in the state where the drum cartridge  1  is attached to the main body frame  101  of the image forming apparatus  100 . This allows a clock signal to be supplied from the controller  102  to the drum circuit board  15  at a constant time interval. As illustrated in  FIG. 6 , the main body side drum clock terminal  31   c  is electrically connected to the multiplexer  34  and the drum memory  151 . 
     The drum detection terminal (cartridge detection terminal)  31   s  is electrically connected to the main body detection terminal  104   s  in the state where the drum cartridge  1  is attached to the main body frame  101  of the image forming apparatus  100 . As illustrated in  FIG. 6 , the drum circuit board  15  has a first drum resistor (cartridge resistor)  331 . The first drum resistor  331  is an electric resistor. The first drum resistor  331  has one end of the first drum resistor  331  connected to the drum detection terminal  31   s  and another end connected to the main body side drum ground terminal  31   g.    
     The drum interrupt terminal  31   i  is electrically connected to the main body interrupt terminal  104   i  in the state where the drum cartridge  1  is attached to the main body frame  101  of the image forming apparatus  100 . As illustrated in  FIG. 6 , the drum interrupt terminal  31   i  is electrically connected to an interrupt output port  342  (described later) of the multiplexer  34 . 
     &lt;5-2. Toner Side Drum Terminal&gt; 
     The plurality of toner side drum terminals  32  are electrically connected to the toner memories  24  of the toner cartridges  2  through the above-described plurality of second connectors  14  in the state where the toner cartridges  2  are attached to the drum frame  12  of the drum cartridge  1 . This allows the drum circuit board  15  and the toner memories  24  to be electrically connected with each other. 
     Hereinafter, four toner cartridges  2  to be attached to the drum cartridge  1  are referred to as a first toner cartridge  2 A, a second toner cartridge  2 B, a third toner cartridge  2 C, and a fourth toner cartridge  2 D. The toner memory  24  for the first toner cartridge  2 A is referred to as a first toner memory  24 A, the toner memory  24  for the second toner cartridge  2 B is referred to as a second toner memory  24 B, the toner memory  24  for the third toner cartridge  2 C is referred to as a third toner memory  24 C, and the toner memory  24  for the fourth toner cartridge  2 D is referred to as a fourth toner memory  24 D. 
     As illustrated in  FIG. 6 , each toner memory  24  has a toner voltage terminal  242   v , a toner ground terminal  242   g , a toner data terminal  242   d , and a toner clock terminal  242   c . Further, each toner memory  24  has a toner resistor  243 . The toner resistor  243  is an electric resistor. The toner resistor  243  has one end connected to the toner voltage terminal  242   v  and another end connected to the toner data terminal  242   d.    
     The plurality of toner side drum terminals  32  include a first group  32 A having four toner side drum terminals  32 , a second group  32 B having four toner side drum terminals  32 , a third group  32 C having four toner side drum terminals  32 , and a fourth group  32 D having four toner side drum terminals  32 . 
     The toner side drum terminals  32  of the first group  32 A are electrically connected to the first toner memory  24 A in the state where the first toner cartridge  2 A is attached to the drum frame  12  of the drum cartridge  1 . The toner side drum terminals  32  of the second group  32 B are electrically connected to the second toner memory  24 B in the state where the second toner cartridge  2 B is attached to the drum frame  12  of the drum cartridge  1 . The toner side drum terminals  32  of the third group  32 C are electrically connected to the third toner memory  24 C in the state where the third toner cartridge  2 C is attached to the drum frame  12  of the drum cartridge  1 . The toner side drum terminals  32  of the fourth group  32 D are electrically connected to the fourth toner memory  24 D in the state where the fourth toner cartridge  2 D is attached to the drum frame  12  of the drum cartridge  1 . 
     The toner side drum terminals  32  of each group include a toner side drum voltage terminal  32   v , a toner side drum ground terminal  32   g , a toner side drum data terminal  32   d , and a toner side drum clock terminal  32   c.    
     The toner side drum voltage terminal  32   v  of each group is electrically connected to the main body side drum voltage terminal  31   v . In the state where one toner cartridge  2  is attached to the drum frame  12  of the drum cartridge  1 , the toner side drum voltage terminal  32   v  of the corresponding group is electrically connected to the toner voltage terminal  242   v  of the toner memory  24  in the toner cartridge  2 . This allows the first voltage to be supplied from the controller  102  to the toner memory  24  through the drum circuit board  15 . 
     The toner side drum ground terminal  32   g  of each group is electrically connected to the main body side drum ground terminal  31   g . In the state where one toner cartridge  2  is attached to the drum frame  12  of the drum cartridge  1 , the toner side drum ground terminal  32   g  of the corresponding group is electrically connected to the toner ground terminal  242   g  of the toner memory  24  in the toner cartridge  2 . This allows the toner ground terminal  242   g  to be grounded. 
     The toner side drum data terminal  32   d  of each group is electrically connected to the multiplexer  34 . In the state where one toner cartridge  2  is attached to the drum frame  12  of the drum cartridge  1 , the toner side drum data terminal  32   d  of the corresponding group is electrically connected to the toner data terminal  242   d  of the toner memory  24  in the toner cartridge  2 . 
     As illustrated in  FIG. 6 , the drum circuit board  15  has a second drum resistor  332 . The second drum resistor  332  is an electric resistor. The second drum resistor has one end connected to the toner side drum data terminal  32   d  and the multiplexer  34 , and another end connected to both of the main body side drum ground terminal  31   g  and the toner side drum ground terminal  32   g.    
     The toner side drum clock terminal  32   c  of each group is electrically connected to the multiplexer  34 . In the state where one toner cartridge  2  is attached to the drum frame  12  of the drum cartridge  1 , the corresponding toner side drum clock terminal  32   c  is electrically connected to the toner clock terminal  242   c  of the toner memory  24 . 
     The toner memory  24  may have such a configuration, in which the toner resistor  243  and an E2PROM, in which information can be written in serial communication and from which information can be read in serial communication, are mounted on a small substrate. In this case, the toner voltage terminal  242   v , toner ground terminal  242   g , toner data terminal  242   d , and toner clock terminal  242   c  which are mounted on the small substrate are connected to the E2PROM, and the toner voltage terminal  242   v  and toner data terminal  242   d  which are mounted on the small substrate are connected to the toner resistor  243 . 
     &lt;5-3. Multiplexer&gt; 
     The multiplexer  34  is a switch circuit for switching among the toner memories  24  to select one of the toner memories  24  as a communication destination. The multiplexer  34  receives a clock signal from the controller  102  through the main body side drum clock terminal  31   c . Further, the multiplexer  34  supplies the input clock signal to the toner memories  24  through the toner side drum clock terminals  32   c.    
     Further, the multiplexer  34  receives an address signal and a data signal from the controller  102  through the main body side drum data terminal  31   d . The address signal is a signal for designating the toner memory  24  of a communication destination. The data signal is a signal indicating various information items to be transmitted to the toner memory  24  of a communication destination. The multiplexer  34  selects one of the four toner side drum data terminals  32   d  according to the received address signal. Then, the multiplexer  34  outputs the received data signal to the toner memory  24  through the selected toner side drum data terminal  32   d.    
     That is, the multiplexer  34  can switch data transmission and/or reception among data transmission and/or reception for the first toner memory  24 A, data transmission and/or reception for the second toner memory  24 B, data transmission and/or reception for the third toner memory  24 C, and data transmission and/or reception for the fourth toner memory  24 D. 
     The multiplexer  34  has four interrupt input ports  341  and one interrupt output port  342  so as to allow the controller  102  to execute interrupt processing. The four interrupt input ports  341  are in one to one correspondence with the four groups  32 A,  32 B,  23 C, and  32 D. Each interrupt input port  341  is connected to the toner side drum data terminal  32   d  and the second drum resistor  332  in the corresponding group. The interrupt output port  342  is connected to the drum interrupt terminal  31   i.    
     When the ground voltage is supplied to at least one of the four interrupt input ports  341 , the multiplexer  34  outputs a first interrupt signal from the interrupt output port  342 . On the other hand, when a second voltage higher than the ground voltage and lower than the first voltage is supplied to all the four interrupt input ports  341 , the multiplexer  34  outputs a second interrupt signal from the interrupt output port  342 . The first interrupt signal is a voltage signal. The second interrupt signal is also a voltage signal, but the value of the voltage of the second interrupt signal is different from that of the voltage of the first interrupt signal. 
     &lt;5-4. Relay of Information by Drum Circuit Board&gt; 
     In the state where the drum cartridge  1  attached with the toner cartridges  2  is attached to the main body frame  101  of the image forming apparatus  100 , the controller  102  and the toner memories  24  are electrically connected with each other through the drum circuit board  15 . With this configuration, the drum circuit board  15  can relay information between the controller  102  and the toner memories  24 . For example, the controller  102  can read information stored in the toner memories  24  through the second harness  17 , the drum circuit board  15 , and the first harness  16 . Further, the controller  102  can write data in the toner memory  24  through the first harness  16 , the drum circuit board  15 , and the second harness  17 . 
     &lt;6. Detection of Presence/Absence of Drum Cartridge&gt; 
     Next, referring to the flow chart illustrated in  FIG. 7 , description will be made with the respect to a process in which the controller  102  of the image forming apparatus  100  determines whether the drum cartridge  1  is attached to the main body frame  101 . 
     The controller  102  of the image forming apparatus  100  determines whether power is switched from OFF to ON or whether the cover  108  is moved from the open position to the closed position in a power-ON state (S 11 ). The controller  102  determines that the cover  108  is moved from the open position to the closed position based on a detection signal from the sensor  109 . 
     When the controller  102  determines that power is switched from OFF to ON or that the cover  108  is moved from the open position to the closed position in the power-ON state (S 11 ; yes), the voltage measurement circuit  102   a  of the controller  102  measures the voltage value of the main body detection terminal  104   s.    
     It is noted that in a case where the drum cartridge  1  is not attached to the main body frame  101 , no current flows through the main body resistor  107 . Thus, the voltage at the main body detection terminal  104   s  has the same potential with the potential of the first voltage at the main body voltage terminal  104   v , which is connected to the main body detection terminal  104   s  through the main body resistor  107 . 
     On the other hand, in a case where the drum cartridge  1  is attached to the main body frame  101 , current flows from the main body voltage terminal  104   v  toward the main body ground terminal  104   g  through: the main body resistor  107 ; main body detection terminal  104   s ; drum detection terminal  31   s ; first drum resistor  331 ; and main body side drum ground terminal  31   g . Thus, the voltage at the main body detection terminal  104   s , which is positioned between the main body resistor  107  and the first drum resistor  331 , becomes a second voltage that is lower than the first voltage and higher than the ground voltage. 
     Accordingly, the controller  102  determines whether the voltage at the main body detection terminal  104   s  measured by the voltage measurement circuit  102   a  is the first voltage or the second voltage (S 12 , first determination process). When determining that the voltage at the main body detection terminal  104   s  is the first voltage (S 12 : no), the controller  102  determines that the main body detection terminal  104   s  and the drum detection terminal  31   s  are not connected with each other (S 13 ). That is, the controller  102  determines that the drum cartridge  1  is not attached to the main body frame  101 . 
     Then, the controller  102  instructs the display  103  to display the result of the first determination process (S 14 , first display control processing). Specifically, the controller  102  instructs the display  103  to display a message indicating that the drum cartridge  1  is not attached to the main body frame  101 . 
     On the other hand, when determining that the voltage at the main body detection terminal  104   s  measured by the voltage measurement circuit  102   a  is the second voltage (S 12 : yes), the controller  102  determines that the main body detection terminal  104   s  and the drum detection terminal  31   s  are connected with each other (step S 15 ). That is, the controller  102  determines that the drum cartridge  1  is attached to the main body frame  101 . 
     Then, the controller  102  instructs the display  103  to display the result of the first determination process (S 16 , first display control process). Specifically, the controller  102  instructs the display  103  to display a message indicating that the drum cartridge  1  is attached to the main body frame  101 . 
     When determining in the first determination process that the main body detection terminal  104   s  and the drum detection terminal  31   s  are connected with each other, the controller  102  determines, after the first display control process, whether the controller is able to communicate with the information stored in the drum memory  151  (S 17 , second determination process). That is, the controller  102  determines whether the controller  102  is able to communicate with the information stored in the drum memory  151  through the main body data terminal  104   d  and the main body side drum data terminal  31   d.    
     In the second determination process, the controller  102  transmits authentication information to the drum memory  151 , for example. Then, when the controller  102  receives a response value from the drum memory  151 , the controller  102  determines that the controller  102  is able to communicate with the information stored in the drum memory  151 . On the other hand, when the controller  102  does not receive a response value from the drum memory  151 , the controller  102  determines that the controller  102  is unable to communicate with the information stored in the drum memory  151 . 
     When determining that the controller  102  is unable to communicate with the information stored in the drum memory  151  (S 17 : no), the controller  102  instructs the display  103  to display a determination result indicating that the controller  102  is unable to communicate with the information stored in the drum memory  151  (S 18 , second display control process). Specifically, the controller  102  instructs the display  103  to display a message indicating that the controller  102  is unable to communicate with information stored in the drum memory  151 . 
     On the other hand, when determining that the controller is able to communicate with the information stored in the drum memory  151  (S 17 : yes), the controller  102  reads the information stored in the drum memory  151  through the main body side drum data terminal  31   d  and the main body data terminal  104   d  (S 19 ). Specifically, the controller  102  reads, from the drum memory  151 , at least one of information identifying the drum cartridge  1  and information indicating characteristics of the drum cartridge  1 . 
     As described above, in the first determination process, the controller  102  of the image forming apparatus  100  can determine whether the main body detection terminal  104   s  and the drum detection terminal  31   s  are connected with each other based on a voltage at the main body detection terminal  104   s . Further, in the first determination process, the controller  102  can determine whether the drum cartridge  1  is attached to the main body frame  101  based on whether the main body detection terminal  104   s  and the drum detection terminal  31   s  are connected with each other. Thus, the controller  102  can determine whether the drum cartridge  1  is attached to the main body frame  101  without communicating with the drum memory  151 . 
     &lt;7. Detection of Presence/Absence of Toner Cartridge&gt; 
     Next, referring to the flow chart illustrated in  FIG. 8 , description will be made with the respect to a process in which the controller  102  of the image forming apparatus  100  determines whether the toner cartridge  2  is attached to the drum frame  12 . 
     The controller  102  of the image forming apparatus  100  determines whether power is switched from OFF to ON or whether the cover  108  is moved from the open position to the closed position in the power-ON state (S 21 ). The controller  102  determines that the cover  108  is moved from the open position to the closed position based on a detection signal from the sensor  109 . 
     When the controller  102  determines that power is switched from OFF to ON or that the cover  108  is moved from the open position to the closed position in the power-ON state (S 21 : yes), the signal detection circuit  102   b  of the controller  102  detects an interrupt signal received by the main body interrupt terminal  104   i.    
     Here, a case where the toner cartridge  2  is not attached to the corresponding toner cartridge holder  121  of the drum frame  12  and a case where the toner cartridge  2  is attached to the corresponding toner cartridge holder  121  will be considered. 
     In the case where the toner cartridge  2  is not attached to the corresponding toner cartridge holder  121 , the toner voltage terminal  242   v  of the toner cartridge  2  is not connected to the toner side drum voltage terminal  32   v  of the drum circuit board  15  and, similarly, the toner ground terminal  242   g  of the toner cartridge  2  is not connected to the toner side drum ground terminal  32   g  of the drum circuit board  15 , and the toner data terminal  242   d  of the toner cartridge  2  is not connected to the toner side drum data terminal  32   d  of the drum circuit board  15 . Therefore, no current flows through the second drum resistor  332  connected to the toner side drum data terminal  32   d . Thus, the voltage at the toner side drum data terminal  32   d  becomes the same potential as the potential of the ground voltage at the main body side drum ground terminal  31   g , which is connected to the toner side drum data terminal  32   d  through the second drum resistor  332 . The ground voltage at the toner side drum data terminal  32   d  is input to the interrupt input port  341  of the multiplexer  34 . 
     On the other hand, in the case where the toner cartridge  2  is attached to the toner cartridge holder  121 , the toner voltage terminal  242   v  of the toner cartridge  2  is connected to the toner side drum voltage terminal  32   v  of the drum circuit board  15 . The toner ground terminal  242   g  of the toner cartridge  2  is connected to the toner side drum ground terminal  32   g  of the drum circuit board  15 . The toner data terminal  242   d  of the toner cartridge  2  is connected to the toner side drum data terminal  32   d  of the drum circuit board  15 . Therefore, current flows from the main body voltage terminal  104   v  toward the main body ground terminal  104   g  through: the main body side drum voltage terminal  31   v ; toner side drum voltage terminal  32   v ; toner voltage terminal  242   v ; toner resistor  243 ; toner data terminal  242   d ; toner side drum data terminal  32   d ; second drum resistor  332 ; and main body side drum ground terminal  31   g . Thus, the voltage at the toner side drum data terminal  32   d , which is positioned between the toner resistor  243  and the second drum resistor  332 , becomes the second voltage that is lower than the first voltage and higher than the ground voltage. The second voltage at the toner side drum data terminal  32   d  is input to the interrupt input port  341  of the multiplexer  34 . In other words, the first voltage supplied from the main body voltage terminal  104   v  is dropped by the toner resistor  243  to become the second voltage, which in turn is input to the interrupt input port  341  of the multiplexer  34 . 
     Thus, when at least one of the four toner cartridge holders  121  is attached with no toner cartridge  2 , the ground voltage is input to at least one of the four interrupt input ports  341  of the multiplexer  34 . In this case, the multiplexer  34  outputs the first interrupt signal from the interrupt output port  342  to the main body interrupt terminal  104   i  through the drum interrupt terminal  31   i.    
     On the other hand, when all the four toner cartridge holders  121  are attached with the toner cartridges  2 , the second voltage is input to all the four interrupt input ports  341  of the multiplexer  34 . In this case, the multiplexer  34  outputs the second interrupt signal, whose voltage value is different from that of the first interrupt signal, from the interrupt output port  342  to the main body interrupt terminal  104   i  through the drum interrupt terminal  31   i.    
     Accordingly, the controller  102  determines whether the interrupt signal detected by the signal detection circuit  102   b  is the first interrupt signal or second interrupt signal (S 22 , third determination process). In other words, the controller  102  determines whether the main body voltage terminal  104   v  and the toner voltage terminal  242   v  are electrically connected with each other via the main body side drum voltage terminal  31   v  and the toner side drum voltage terminal  32   v . When determining that the interrupt signal detected by the signal detection circuit  102   b  is the first interrupt signal (S 22 : no), the controller  102  determines that at least one of the toner cartridge holders  121  in the drum frame  12  is attached with no toner cartridge  2  (S 23 ). 
     Then, the controller  102  instructs the display  103  to display the result of the third determination process (S 24 , third display control process). Specifically, the controller  102  instructs the display  103  to display a message (first error message) indicating that at least one toner cartridge holder  121  of the drum frame  12  is attached with no toner cartridge  2 . 
     On the other hand, when determining, in the third determination process, that the interrupt signal detected by the signal detection circuit  102   b  is the second interrupt signal (S 22 : yes), the controller  102  determines that all the toner cartridge holders  121  of the drum frame  12  are attached with the toner cartridges  2  (S 25 ). 
     Then, the controller  102  instructs the display  103  to display the result of the third determination process (S 26 , third display control process). Specifically, the controller  102  instructs the display  103  to display a message indicating that all the toner cartridge holders  121  of the drum frame  12  are attached with the toner cartridges  2 . 
     When determining, in the third determination process, that all the toner cartridge holders  121  of the drum frame  12  are attached with the toner cartridges  2 , the controller  102  determines, after the third display control process, whether the controller  102  is able to communicate with the information stored in all of the four toner memories  24  (S 27 , fourth determination process). That is, the controller  102  determines whether the controller  102  is able to communicate with information stored in the toner memories  24  through the drum circuit board  15 . 
     In the fourth determination process, the controller  102  transmits authentication information to each of the four toner memories  24 , for example. Then, when the controller  102  receives a response value from each of the four toner memories  24 , the controller  102  determines that the controller  102  is able to communicate with the information stored in each of the four toner memories  24 . On the other hand, when the controller  102  receives no response value from at least one toner memory  24 , the controller  102  determines that the controller  102  is unable to communicate with the information stored in the at least one toner memory  24 . 
     When determining that the controller  102  is unable to communicate with the information stored in the at least one toner memory  24  (S 27 : no), the controller  102  instructs the display  103  to display a determination result indicating that the controller  102  is unable to communicate with the information stored in at least one toner memory  24  (S 28 , fourth display control process). Specifically, the controller  102  instructs the display  103  to display a message (second error message) indicating that the controller  102  is unable to communicate with information stored in at least one toner memory  24 . 
     On the other hand, when determining that the controller  102  is able to communicate with the information stored in all of the four toner memories  24  (S 27 : yes), the controller  102  reads information stored in each of the four toner memories  24  through the drum circuit board  15  (S 29 ). Specifically, the controller  102  reads, from the toner memory  24  of each toner cartridge  2 , at least one of information for identifying the toner cartridge  2  and information indicating characteristics of the toner cartridge  2 . 
     As described above, in the third determination process, the controller  102  of the image forming apparatus  100  determines that the toner cartridge  2  is not attached to the toner cartridge holder  121  of the drum frame  12  when the second voltage is not supplied to the interrupt input port  341  of the multiplexer  34  through the toner memory  24  in the state where the interrupt input port  341  of the multiplexer  34  is electrically connected to the main body ground terminal  104   g . Further, in the third determination process, the controller  102  determines that the toner cartridge  2  is attached to the toner cartridge holder  121  of the drum frame  12  when the second voltage is supplied to the interrupt input port  341  of the multiplexer  34  through the toner memory  24 . 
     Thus, the controller  102  can determine whether the toner cartridge  2  is attached to the drum frame  12  without transmitting and receiving data with the toner memory  24 . 
     Further, in the image forming apparatus  100 , the multiplexer  34  outputs the first interrupt signal to the controller  102  when the second voltage is not supplied to the interrupt input port  341  of the multiplexer  34  through the toner memory  24  in the state where the interrupt input port  341  of the multiplexer  34  is electrically connected to the main body ground terminal  104   g . Further, in the image forming apparatus  100 , the multiplexer  34  outputs the second interrupt signal to the controller  102  when the second voltage is supplied to the interrupt input port  341  of the multiplexer  34  through the toner memory  24 . 
     Thus, when the first interrupt signal is output from the multiplexer  34 , the controller  102  can determine that the toner cartridge  2  is not attached to the toner cartridge holder  121  of the drum frame  12 . On the other hand, when the second interrupt signal is output from the multiplexer  34 , the controller  102  can determine that the toner cartridge  2  is attached to the toner cartridge holder  121  of the drum frame  12 . 
     Further, the controller  102  of the image forming apparatus  100  determines that at least one toner cartridge holder  121  of the drum frame  12  is attached with no toner cartridge  2  when the second voltage is not supplied to the interrupt input port  341  of the multiplexer  34  through at least one of the plurality of toner memories  24  in the state where the interrupt input port  341  of the multiplexer  34  is electrically connected to the main body ground terminal  104   g . Further, the controller  102  determines that all the toner cartridge holders  121  of the drum frame  12  are attached with the toner cartridges  2  when the second voltages are supplied to all the plurality of interrupt input ports  341  of the multiplexer  34  through the toner memories  24 . As described above, the controller  102  can determine whether all the toner cartridge holders  121  of the drum frame  12  are attached with the toner cartridges  2 . 
     Further, the controller  102  of the image forming apparatus  100  instructs the display  103  to display messages such that the contents of the messages are different in the case where the toner cartridge holder  121  is attached with no toner cartridge  2  and in the case where the controller  102  is unable to communicate with the toner memory  24  of the toner cartridge  2  attached to the toner cartridge holder  121 . This allows the controller to display an error state in more detail. 
     &lt;8. Modifications&gt; 
     While the one embodiment has been described above, the present disclosure is not limited to the above-described embodiment. Hereinafter, various modifications will be described focusing on differences from the above-described embodiment. 
     &lt;8-1. First Modification&gt; 
       FIG. 9  is a block diagram illustrating electrical connection between the controller  102 , the drum circuit board  15 , and the toner memory  24  according to a first modification. The first modification differs from the above embodiment in the manner how the main body resistor  107  and the first drum resistor  331  are connected to other components. 
     The main body resistor  107  according to the first modification is configured such that the main body resistor  107  has one end connected to the main body detection terminal  104   s  and another end connected to the main body ground terminal  104   g . The first drum resistor  331  according to the first modification is configured such that the drum resistor  331  has one end connected to the drum detection terminal  31   s  and another end connected to the main body side drum voltage terminal  31   v.    
     When the drum cartridge  1  is not attached to the main body frame  101 , no current flows through the main body resistor  107 . Thus, the voltage at the main body detection terminal  104   s  has the same potential as the potential of the ground voltage at the main body ground terminal  104   g , which is connected to the main body detection terminal  104   s  through the main body resistor  107 . 
     On the other hand, when the drum cartridge  1  is attached to the main body frame  101 , current flows from the main body voltage terminal  104   v  toward the main body ground terminal  104   g  through: the main body side drum voltage terminal  31   v ; first drum resistor  331 ; drum detection terminal  31   s ; main body detection terminal  104   s ; and main body resistor  107 . Thus, the voltage at the main body detection terminal  104   s , which is positioned between the first drum resistor  331  and the main body resistor  107 , becomes the second voltage that is lower than the first voltage and higher than the ground voltage. 
     In the first determination process, the controller  102  determines whether the voltage at the main body detection terminal  104   s  measured by the voltage measurement circuit  102   a  is the ground voltage or second voltage. When determining that the voltage at the main body detection terminal  104   s  is the ground voltage, the controller  102  determines that the main body detection terminal  104   s  and the drum detection terminal  31   s  are not connected with each other. That is, the controller  102  determines that the drum cartridge  1  is not attached to the main body frame  101 . 
     On the other hand, when determining, in the first determination process, that the voltage at the main body detection terminal  104   s  is the second voltage, the controller  102  determines that the main body detection terminal  104   s  and the drum detection terminal  31   s  are connected with each other. That is, the controller  102  determines that the drum cartridge  1  is attached to the main body frame  101 . 
     In this first modification as well as the above-described embodiment, the controller  102  can determine whether the drum cartridge  1  is attached to the main body frame  101  based on the voltage at the main body detection terminal  104   s . Thus, the controller  102  can determine whether the drum cartridge  1  is attached to the main body frame  101  without exchanging data with the drum memory  151 . 
     &lt;8-2. Second Modification&gt; 
       FIG. 10  is a block diagram illustrating electrical connection between the controller  102 , the drum circuit board  15 , and the toner memories  24  according to a second modification. The second modification differs from the above-described embodiment in that a thermistor  331   t  is used as the first drum resistor  331 . 
     The thermistor  331   t  is a temperature sensor including an electric resistor. The resistance value of the thermistor  331   t  changes according to the temperature. The thermistor  331   t  has one end connected to the drum detection terminal  31   s  and another end connected to the main body side drum ground terminal  31   g . Thus, the controller  102  can determine whether the drum cartridge  1  is attached to the main body frame  101  by performing the first determination process in the same manner as in the above-described embodiment. 
     Further, in this second modification, the resistance value of the thermistor  331   t  changes according to the temperature. Thus, when the drum cartridge  1  is attached to the main body frame  101 , the value of the second voltage at the main body detection terminal  104   s  also changes according to the temperature. This allows the controller  102  to detect the temperature inside the main body frame  101  based on the value of the second voltage measured by the voltage measurement circuit  102   a.    
     In the second modification, the thermistor  331   t  serves both as the first drum resistor  331  and the temperature sensor. This eliminates the need to separately provide the first drum resistor  331  and the temperature sensor, allowing reduction in the number of components in the drum circuit board  15 . 
     &lt;8-3. Third Modification&gt; 
       FIG. 11  is a block diagram illustrating electrical connection between the controller  102 , the drum circuit board  15 , and one toner memory  24  according to a third modification. The third modification differs from the above-described embodiment in the following respects: the number of the toner cartridges  2  that can be attached to the drum frame  12  is one; the controller  102  has a second main body resistor  107   t , a second main body detection terminal  104   t , and a second voltage measurement circuit  102   t ; the drum circuit board  15  has a main body side drum detection terminal  31   t  and a toner side drum detection terminal  32   t ; and the toner memory  24  has a toner detection terminal  242   t.    
     The second main body resistor  107   t  has one end connected to the second main body detection terminal  104   t  and another end connected to the main body voltage terminal  104   v . The main body side drum detection terminal  31   t  is electrically connected to the second main body detection terminal  104   t  in the state where the drum cartridge  1  is attached to the main body frame  101  of the image forming apparatus  100 . The toner side drum detection terminal  32   t  is electrically connected to the main body side drum detection terminal  31   t . The toner detection terminal (cartridge detection terminal)  242   t  is electrically connected to the toner side drum detection terminal  32   t  in the state where the toner cartridge  2  is attached to the drum frame  12 . The toner resistor  243  (cartridge resistor) has one end connected to the toner detection terminal  242   t  and another end connected to the toner ground terminal  242   g . The second voltage measurement circuit  102   t  can measure the voltage at the second main body detection terminal  104   t.    
     When the toner cartridge  2  is not attached to the drum frame  12 , no current flows through the second main body resistor  107   t . Thus, the voltage at the second main body detection terminal  104   t  has the same potential as the first voltage at the main body voltage terminal  104   v , which is connected to the main body detection terminal  104   t  through the main body resistor  107 . 
     On the other hand, when the toner cartridge  2  is attached to the drum frame  12 , current flows from the main body voltage terminal  104   v  toward the main body ground terminal  104   g  through: the second main body resistor  107   t ; second main body detection terminal  104   t ; main body side drum detection terminal  31   t ; toner side drum detection terminal  32   t ; toner detection terminal  242   t ; toner resistor  243 ; toner ground terminal  242   g ; toner side drum ground terminal  32   g ; and main body side drum ground terminal  31   g . Thus, the voltage at the second main body detection terminal  104   t , which is positioned between the second main body resistor  107   t  and the toner resistor  243 , is the second voltage that is lower than the first voltage and higher than the ground voltage. 
     In the third determination process, the controller  102  determines whether the voltage at the second main body detection terminal  104   t  measured by the second voltage measurement circuit  102   t  is the first voltage or second voltage. That is, the controller  102  determines, in S 22 , whether the voltage at the second main body detection terminal  104   t  measured by the second voltage measurement circuit  102   t  is the first voltage or second voltage. In other words, the controller  102  determines whether the main body detection terminal  104   t  and the toner detection terminal  242   t  are electrically connected with each other via the main body side drum detection terminal  31   t  and the toner side drum detection terminal  32   t . When determining that the voltage at the second main body detection terminal  104   t  is the first voltage, the controller  102  determines that the toner side drum detection terminal  32   t  and the toner detection terminal  242   t  are not connected with each other. That is, the controller  102  determines that the toner cartridge  2  is not attached to the drum frame  12 . 
     On the other hand, when determining, in the third determination process, that the voltage at the second main body detection terminal  104   t  measured by the second voltage measurement circuit  102   t  is the second voltage, the controller  102  determines that the toner side drum detection terminal  32   t  and the toner detection terminal  242   t  are connected with each other. That is, the controller  102  determines that the toner cartridge  2  is attached to the drum frame  12 . 
     As described above, in the third determination process, the controller  102  of the image forming apparatus  100  can determine whether the toner side drum detection terminal  32   t  and the toner detection terminal  242   t  are connected with each other based on the amount of the voltage at the second main body detection terminal  104   t . Further, in the third determination process, the controller  102  can determine whether the toner cartridge  2  is attached to the drum frame  12  based on whether the toner side drum detection terminal  32   t  and the toner detection terminal  242   t  are connected with each other. Thus, the controller  102  can determine whether the toner cartridge  2  is attached to the drum frame  12  without communicating with the toner memory  24 . 
     &lt;8-4. Fourth Modification&gt; 
       FIG. 12  is a block diagram illustrating electrical connection between the controller  102 , the drum circuit board  15 , and the toner memories  24  according to a fourth modification. In FIG.  12 , showing of the data terminals and clock terminals is omitted. The fourth modification differs from the above-described embodiment in the following respects: the controller  102  has a second main body resistor  107   t , a second main body detection terminal  104   t , and a second voltage measurement circuit  102   t ; the drum circuit board  15  has a main body side drum detection terminal  31   t , four toner side drum detection terminals  32   t , and four third drum resistors  333 ; and each of the toner memories  24  has a toner detection terminal  242   t.    
     The resistor  107   t  has one end connected to the second main body detection terminal  104   t  and another end connected to the main body voltage terminal  104   v . The main body side drum detection terminal  3  it is electrically connected to the second main body detection terminal  104   t  in the state where the drum cartridge  1  is attached to the main body frame  101  of the image forming apparatus  100 . The four third drum resistors  333  are connected in parallel. One end of each of the four third drum resistors  333  is connected to the main body side drum detection terminal  31   t , and the other end thereof is connected to the corresponding toner side drum detection terminal  32   t . In each toner memory, the toner detection terminal (cartridge detection terminal)  242   t  is electrically connected to the toner side drum detection terminal  32   t  in the state where the toner cartridge  2  is attached to the drum frame  12 . Further, the toner detection terminal  242   t  is electrically connected to the toner ground terminal  242   g . The second voltage measurement circuit  102   t  can measure the voltage at the second main body detection terminal  104   t.    
     When no toner cartridge  2  is attached to the drum frame  12 , no current flows through the second main body resistor  107   t . Thus, the voltage at the second main body detection terminal  104   t  has the same potential as the first voltage at the main body voltage terminal  104   v , which is connected to the second main body detection terminal  104   t  through the main body resistor  107 . 
     On the other hand, when at least one toner cartridge  2  is attached to the drum frame  12 , current flows from the main body voltage terminal  104   v  toward the main body ground terminal  104   g  through: the second main body resistor  107   t ; second main body detection terminal  104   t ; main body side drum detection terminal  3  it; one of the third drum resistors  333  that is connected to the toner memory  24  of the attached toner cartridge  2 ; toner side drum detection terminal  32   t ; toner detection terminal  242   t ; toner ground terminal  242   g ; toner side drum ground terminal  32   g ; and main body side drum ground terminal  31   g . Thus, the voltage at the second main body detection terminal  104   t , which is positioned between the second main body resistor  107   t  and the third drum resistor  333 , becomes the second voltage that is lower than the first voltage and higher than the ground voltage. 
     In the fourth modification, resistance values of the four third drum resistors  333  differ from one another. Further, resultant resistance values of parallel combinations of any two, three or four of the four third drum resistors  333  differ from one another. With such a configuration, the voltage value of the second voltage changes depending on a combination of the third drum resistors  333 , through which current flows. 
     In the third determination process, the controller  102  determines whether the voltage at the second main body detection terminal  104   t  measured by the second voltage measurement circuit  102   t  is the first voltage or second voltage. That is, the controller  102  determines, in S 22 , whether the voltage at the second main body detection terminal  104   t  measured by the second voltage measurement circuit  102   t  is the first voltage or second voltage. In other words, the controller  102  determines whether the main body detection terminal  104   t  and the toner detection terminal  242   t  are electrically connected with each other via the main body side drum detection terminal  31   t  and the toner side drum detection terminal  32   t . When determining that the voltage at the second main body detection terminal  104   t  is the first voltage, the controller  102  determines that none of the toner side drum detection terminals  32   t  of the drum circuit board  15  are connected with the toner detection terminal  242   t . That is, the controller  102  determines that the drum frames  12  is attached with no toner cartridges  2 . 
     On the other hand, when determining, in the third determination process, that the voltage at the second main body detection terminal  104   t  measured by the second voltage measurement circuit  102   t  is the second voltage, the controller  102  determines that at least one of the toner side drum detection terminals  32   t  of the drum circuit board  15  is connected with the toner detection terminal  242   t . That is, the controller  102  determines that at least one toner cartridge  2  is attached to the drum frame  12 . 
     In this case, the controller  102  further determines a combination of the attached toner cartridges  2  based on the voltage value of the second voltage. Specifically, the correspondence relationship between a plurality of combinations of the toner cartridges  2  to be attached and voltage values of the second voltage are previously stored in the main body memory  106  of the controller  102 . The controller  102  determines, in the third determination process, a combination of the attached toner cartridges  2  based on the voltage value of the second voltage measured by the second voltage measurement circuit  102   t  and the correspondence relationship read from the main body memory  106 . 
     &lt;8-5. Other Modifications&gt; 
     The structures, the circuit configurations and processing procedures in the above-described embodiments and modifications are merely examples. Various elements appearing in the above-described embodiments and modifications may be replaced with other known elements without departing from the scope of the disclosure. Further, various elements appearing in the above-described embodiments and modifications may be appropriately combined within a range in which inconsistency does not occur. 
     While the description has been made in detail with reference to the specific embodiment, it would be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the disclosure. 
     For example, the first drum resistor  331  in the first modification ( FIG. 9 ) may be replaced with a thermistor  331   t  as in the second modification ( FIG. 10 ).