Abstract:
An information processing apparatus serves as a host unit for communicating to a plurality of printing apparatuses via a network. Each of the printing apparatuses includes internal components that are set in a sleep state when power supply to the components is reduced or in a print-ready state when power is supplied to the components. The information processing apparatus includes a unit for requesting status information of each of the plurality of printing apparatuses via the network, a unit for receiving the requested status information from each of the plurality of printing apparatuses, and a unit for identifying each of the plurality of printing apparatuses as being either in the sleep state or in the print-ready state, based on the status information. The information processing apparatus also includes a unit for controlling a display status of each of the plurality of printing apparatuses on a same window, so as to indicate each printing apparatus as being in the sleep state or in the print-ready state, based on respective identification results.

Description:
This application is a division of application Ser. No. 08/958,740, filed on Oct. 27, 1997, now U.S. Pat. No. 5,937,148 which is a continuation of application Ser. No. 08/354,116, filed on Dec. 6, 1994 now abandonded. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a printing apparatus having a power saving function (sleep mode) for suppressing power consumption in a non-printing state, a system having the same, and a method of controlling the printing apparatus. 
     In recent years, printing apparatuses of this type, e.g., page printers represented by laser beam printers have become rapidly widespread. 
     Generally, an apparatus of this type is constituted by a printer controller for receiving printing data to generate a printing image and at the same time controlling the entire apparatus, and a printer engine for actually performing printing. Since the printer engine has a thermal fixing unit, the power consumption is undesirably increased. 
     For this reason, in a printing standby state, in other words, when a predetermined period of time has elapsed after supply of printing data from a host unit (e.g., host computer) is cut off, power to the printer engine, particularly to the thermal fixing unit is stopped, thereby appropriately suppressing the power consumption. That is, this printer has a sleep mode (or power save mode). 
     Setting and canceling of the sleep mode are controlled by the printer controller (CPU in the printer controller). More specifically, upon power-on, or when a predetermined period of time has elapsed after completion of printing processing, and no further printing data is received, power supply to the printer engine is stopped. If printing data is received in the sleep mode, power supply to the printer engine is resumed. 
     Although the power consumption can be surely reduced in the sleep mode as compared to an actual printing mode, power supply to the printer controller never stops. Additionally, the CPU and various circuits requiring a large power consumption are connected to the printer controller through buses. Taking these factors into consideration, no sufficient power saving effect can be obtained yet. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to solve the above problem, and the first to eighth inventions according to the present invention have as their object to provide a printing apparatus in which an interface section for performing communication processing with a host unit is separated from a controller section, and the interface section controls the power supply states of the controller section and a printer engine section to control the power supply states of the controller section and the printer engine section, both of which have a large power loss, such that the printing apparatus itself further saves power consumption in a sleep state while ensuring a communication state with the host unit. 
     The first invention according to the present invention comprises an interface section for performing data communication with a host unit, a controller section for generating a printing image based on printing data sent from the host unit through the interface section, an engine section for performing recording on a recording medium on the basis of the printing image from the controller section, and a power supply for always supplying power to the interface section while a power supply switch is in an ON state, wherein the interface section has control means for controlling power supply from the power supply to the controller section and the engine section on the basis of data received from the host unit. 
     In the second invention according to the present invention, the control means controls power supply such that power supply from the power supply to the controller section is started upon reception of a predetermined command from the host unit, and power supply from the power supply to the controller section is stopped upon reception of a predetermined command from the controller section. 
     In the third invention according to the present invention, the interface section has informing means for informing a status of a printing apparatus main body to the host unit. 
     In the fourth invention according to the present invention, the interface section communicates with a plurality of host units through a network. 
     In the fifth invention according to the present invention, the host unit preferentially selects a printing apparatus whose printing apparatus main body is set in a standby state, which is informed by the informing means, before a printing apparatus in a sleep state. 
     In the sixth invention according to the present invention, when the host unit recognizes that a plurality of printing apparatuses are set in the standby state, the host unit sends a command for setting one of the printing apparatuses in the sleep state to the interface section. 
     In the seventh invention according to the present invention, the interface section can be freely attached/detached to/from the printing apparatus main body. 
     In the eighth invention according to the present invention, the interface section can be externally connected through an external interface port of a printing apparatus main body. 
     In the first invention according to the present invention, the control means of the interface section controls power supply from the power supply to the controller section and the engine section on the basis of data received from the host unit to limit power supply to the controller section and the engine section in the sleep state except for power supply in the interface section, thereby further saving power. 
     In the second invention, the control means controls power supply such that power supply from the power supply to the controller section is started upon reception of a predetermined command from the host unit, and power supply from the power to the controller section is stopped upon reception of a predetermined command from the controller section. In accordance with a command from the host unit, the state of the printing apparatus can be reversibly switched from the sleep state to the standby state or from the standby state to the sleep state. 
     In the third invention, the informing means of the interface section informs the status of the printing apparatus main body to the host unit such that the host unit can properly determine the current printer status of the printing apparatus. 
     In the fourth invention, the interface section communicates with the host unit through a network. Upon reception of a command from any one of the host units, power supply to the controller section and the engine section in the sleep state can be limited except for power supply in the interface section, thereby further saving power. 
     In the fifth invention, in accordance with information from the interface section, the host unit preferentially selects a printing apparatus whose printing apparatus main body is set in the standby state before a printing apparatus in the sleep state, thereby determining a printing apparatus capable of performing printing processing as quickly as possible. 
     In the sixth invention, when the host unit recognizes that a plurality of printing apparatuses whose printing apparatus main bodies are set in the standby state are present, the host unit sends a command for setting one of the printing apparatuses in the sleep state to the interface section. With this operation, regardless of changes in status of each printing apparatus, a printing apparatus capable of performing printing processing can be determined as quickly as possible while printing apparatuses not subjected to printing are set in the sleep state. 
     In the seventh invention, the interface section can be freely attached/detached to/from the printing apparatus main body, thereby coping with expansion or modification of the interface section. 
     In the eighth invention, the interface section can be externally connected through the external interface port of the printing apparatus main body, thereby externally expanding the function of the interface section to a conventional printing apparatus. 
     Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing the circuit arrangement of a printing apparatus according to an embodiment of the present invention; 
     FIG. 2 is a sectional view for explaining an example of a printing apparatus shown in FIG. 1; 
     FIG. 3 is a flow chart showing an embodiment of the first power saving control method of the printing apparatus according to the present invention; 
     FIG. 4 is a flow chart showing an embodiment of the second power saving control method of the printing apparatus according to the present invention; 
     FIG. 5 is a flow chart showing an example of printing data output processing procedures in the printing apparatus according to the present invention; 
     FIG. 6 is a flow chart showing printing processing procedures in a host computer of the third embodiment; 
     FIG. 7 is a view showing an example of a display screen in the host computer of the third embodiment; 
     FIG. 8 is a flow chart showing printing processing procedures in the host computer of the fourth embodiment; and 
     FIG. 9 is a block diagram of the host computer of the embodiments. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment according to the present invention will be described below in detail with reference to the accompanying drawings. 
     &lt;Description of Apparatus Arrangement&gt; 
     FIG. 1 is a block diagram showing the circuit arrangement of a printing apparatus showing an embodiment of the present invention. 
     Referring to FIG. 1, reference numerals  100 - 1  and  100 - 2  denote printing apparatus main bodies. As shown in FIG. 1, the printing apparatuses of this embodiment are placed in an environment in which a plurality of printing apparatuses are connected to a plurality of host computers  130 - 1  and  130 - 2 . 
     The printing apparatus main body of this embodiment is mainly constituted by a controller section  110  and an engine section  120 . 
     The controller section  110  serves as a printer controller for receiving printing data, a control command, and the like from an external equipment, accordingly preparing bit map data in an image memory (not shown), and transferring the data to the engine section  120  as a video signal. The engine section  120  receives the video signal from the controller section  110  and forms a visible image on a sheet surface from the video signal (to be described later in detail). 
     The controller section  110  communicates with the engine section  120  to externally inform the status of the engine section  120 . 
     The controller section  110  will be described below in detail. 
     The controller section  110  has a host interface processor (I/O processor; to be referred to as an IOP hereinafter)  111 , a CPU  114 , a ROM  115 , a RAM  116 , a data bus (bus)  118 , and a local bus  119 . 
     As described above, although not illustrated, an image memory for developing a bit map image, an interface to the engine section  120 , and an interface to an operation panel (not shown) are also provided on the bus  118 . 
     The IOP  111  transmits/receives data to/from an external apparatus (host computer) and has an intelligence to some extent as described later. A program for interpreting printing data in various printer languages to generate a bit image, a program for controlling the entire apparatus, and font data are stored in the ROM  115 . 
     The RAM  116  always receives power during the power-ON state of the apparatus main body and is used as a work area of the CPU  114 . The RAM  116  is also used as a work area for information processing, or used to save various printing parameters and store the status information of the printing apparatus. 
     Data, an address, and a control signal, which are transmitted in the controller, flow through the bus  118 . The IOP  111  can refer to or write-access the RAM  116  through the local bus  119  (not through the CPU  114  and the bus  118 ) which is directly connected to the RAM  116 . 
     Reference numeral  140  denotes a power supply turned on/off by a power supply switch (not shown). Normally, power having a necessary potential is always supplied to an interface section  150 . 
     A correspondence between this embodiment and each means of the first to eighth inventions and the function thereof will be described below with reference to FIG.  1 . 
     The first invention has the interface section  150  for performing data communication with the host unit  130 - 1  or  130 - 2 , the controller section  110  for generating a printing image based on printing data sent from the host unit  130 - 1  or  130 - 2  through the interface section  150 , the engine section  120  for performing recording on a recording medium on the basis of the printing image from the controller section  110 , and the power supply  140  for always supplying power to the interface section  150  during the ON state of the power supply switch. The interface section  150  has the control means (IOP  111 ) for controlling power supply from the power supply  140  to the controller section  110  and the engine section  120  on the basis of data received from the host unit  130 - 1  or  130 - 2 . The IOP  111  controls power supply from the power supply  140  to the controller section  110  and the engine section  120  on the basis of the data received from the host unit  130 - 1  or  130 - 2  to limit power supply to the controller section  110  and the engine section  120  in a sleep state except for power supply in the interface section  150 , thereby further saving power. 
     In the second invention, the control means (IOP  111 ) controls power supply such that power supply from the power supply  140  to the controller  110  is started upon reception of a predetermined command from the host unit  130 - 1  or  130 - 2 , and power supply from the power supply  140  to the controller section  110  is stopped upon reception of a predetermined command from the controller section  110 . In accordance with a command from the host unit  130 - 1  or  130 - 2 , the status of the printing apparatus main body  100 - 1  or  100 - 2  can be reversibly switched from the sleep state to the standby state or from the standby state to the sleep state. 
     In the third invention, the interface section  150  has an informing means for informing the status of the printing apparatus main body to the host unit. The informing means (IOP  111 ) of the interface section  150  informs the status of the printing apparatus main body to the host unit  130 - 1  or  130 - 2  such that the host unit  130 - 1  or  130 - 2  can properly determine the current printer status of the printing apparatus main body  100 - 1  or  100 - 2 . 
     In the fourth invention, the interface section  150  communicates with the host unit  130 - 1  or  130 - 2  through a network. Upon reception of a command from any one of the host units  130 - 1  and  130 - 2 , power supply to the controller section  110  and the engine section  120  in the sleep state can be limited except for power supply in the interface section  150 , thereby further saving power. 
     In the fifth invention, in accordance with information from the interface section  150 , the host unit  130 - 1  or  130 - 2  preferentially selects a printing apparatus whose printing apparatus main body  100 - 1  or  100 - 2  is set in the standby state before a printing apparatus in the sleep state, thereby determining a printing apparatus capable of performing printing processing as quickly as possible. 
     In the sixth invention, when the host unit  130 - 1  or  130 - 2  recognizes that a plurality of printing apparatuses whose printing apparatus main bodies  100 - 1  and  100 - 2  are set in the standby state are present, the host unit  130 - 1  or  130 - 2  sends a command for setting one of the printing apparatuses in the sleep state to the interface section. With this operation, regardless of changes in status of each printing apparatus, the printing apparatus main body  100 - 1  or  100 - 2  capable of performing printing processing can be determined as quickly as possible while printing apparatuses not subjected to printing are set in the sleep state. 
     In the seventh invention, the interface section  150  can be freely attached/detached to/from the printing apparatus main body  100 - 1  or  100 - 2 , thereby coping with expansion or modification of the interface section  150 . 
     In the eighth invention, the interface section  150  can be externally connected through the external interface port (not shown) of the printing apparatus main body  100 - 1  or  100 - 2 , thereby externally expanding the function of the interface section to a conventional printing apparatus. 
     The engine section  120  of the apparatus of this embodiment will be described below. 
     FIG. 2 is a sectional view for explaining an example of the printing section shown in FIG. 1, which corresponds to, e.g., the engine of a laser beam printer. 
     In the printer of this embodiment, character patterns or fixed formats (form data) can be registered from the host computer. 
     Referring to FIG. 2, reference numeral  100  denotes an apparatus main body. The apparatus main body  100  receives and stores character information (character code), form information, or a macro command supplied from the externally connected host computer, and at the same time prepares a corresponding character pattern or form pattern in accordance with the information, thereby forming an image on recording paper serving as a recording medium. 
     Reference numeral  700  denotes an operation panel having switches, an LCD display, and the like used for an operation. Reference numeral  701  denotes a printer control unit for controlling the entire apparatus main body  100  and analyzing character information and the like supplied from the host computer. 
     The printer control unit  701  mainly converts a character pattern corresponding to character information into a video signal and outputs this video signal to a laser driver  702 . The printer control unit  701  corresponds to the printer controller section  110  shown in FIG.  1 . The laser driver  702  is a circuit for driving a semiconductor laser  703 , which turns on/off a laser beam  704  emitted from the semiconductor laser  703  in accordance with the received video signal. The laser beam  704  is deflected by a rotary polygon mirror  705  in the right and left directions and scanned on an electrostatic drum  706 . With this operation, an electrostatic latent image such as a character pattern is formed on the electrostatic drum  706 . This latent image is developed by a developing unit  707  around the electrostatic drum  706  and then transferred on recording paper. 
     As the recording paper, cut sheets are used. The cut sheets are stored in a sheet cassette  708  mounted in the LBP  100 , carried into the apparatus by a feed roller  709  and convey rollers  710  and  711 , and supplied onto the electrostatic drum  706 . A toner image adhered on the electrostatic drum  706  by the developing unit  707  is transferred on the conveyed recording paper. Thereafter, the recording paper is conveyed toward a fixing unit  712 , and the toner is fixed. Finally, the recording paper is discharged from the apparatus by a discharge roller  713 . 
     FIG. 9 is a block diagram of the host computer shown in FIG.  1 . 
     The host computer has a CPU  91 , a memory  92 , an input unit  93  constituted by a keyboard, a mouse, and the like, a VRAM  94  for storing a display image, a display unit  95  for displaying the image developed by the VRAM  94 , and an interface  96  for sending the printing data to the printing apparatus described in the above embodiment or receiving various information from the printing apparatus. As the interface  96 , a printer interface capable of performing two-way communication or a network interface is used. 
     Programs based on flow charts in FIGS. 5,  6 , and  8  (to be described later) are stored in the memory  92  and executed by the CPU  91 . 
     &lt;Description of Operation&gt; 
     The operation of this embodiment in the above arrangement will be described below. 
     First of all, the operation processing of the CPU  114  of the controller section  110  of this embodiment will be described with reference to a flow chart in FIG. 3. A program based on this flow chart is stored in the ROM  115 , as a matter of course. 
     FIG. 3 is a flow chart showing an embodiment of the first power saving control method of the printing apparatus according to the present invention. Numbers ( 1 ) to ( 7 ) denote steps. 
     When the apparatus is powered on, the initialization processing of various peripheral circuits is performed in step ( 1 ). The flow advances to step ( 2 ) to write information representing a printing standby state at a predetermined address position (to be referred to as a status area hereinafter) in the RAM  116 . Note that, upon reception of printing data, an interrupt signal is generated from the IOP  111  to the CPU  114  of interface section  150 . The CPU  114  receives the printing data in this interrupt processing and performs writing processing of the data in a reception buffer ensured in the RAM  116 . 
     The flow then advances to step ( 3 ) to determine whether the printing data is stored in the reception buffer. If NO in step ( 3 ), the flow advances to step ( 4 ) to determine whether a predetermined period of time has elapsed in a no-reception state. If it is determined that no data is received after that period of time has elapsed, information representing a sleep state is written in the status area of the RAM  116 , and at the same time, a sleep command signal is generated to the IOP  111  of interface section  150  (step ( 5 )). 
     Upon reception of this command, the IOP  111  of interface section  150  cuts off power supply to the CPU  114  connected to the bus  118 , the remaining units, and the engine section  120  (to be described later in detail). Cutting off of the power itself is performed by, e.g., a relay switch, and a detailed description thereof will be omitted. 
     On the other hand, if YES in step ( 3 ), the flow advances to step ( 6 ) to write information representing the printing state in the status area. The flow advances to step ( 7 ) to perform printing processing on the basis of the received data. 
     As a result, three pieces of status information each indicating the printing standby state, the sleep state, and the printing state (busy state) are stored in the status area. 
     The control operation by the IOP  111  of interface section  150  shown in FIG. 1 will be described below with reference to FIG.  4 . 
     Unlike the units connected to the bus  118 , the IOP  111  and the RAM  116  receive power supply during the ON state of the main switch of the apparatus main body regardless of the sleep state. 
     Control processing performed by the IOP  111  is much simpler than that of the CPU  114  as a main unit. The circuits enabled for the operation are also limited, and the number of types of clocks and the like required for the operation can be largely reduced. For this reason, the power consumption can be reduced as compared to a case wherein power is supplied to the controller section  110 . 
     FIG. 4 is a flow chart showing an embodiment of the second power saving control method of the printing apparatus according to the present invention. Numbers ( 11 ) to ( 18 ) denote steps. 
     In step ( 11 ), it is determined whether data is received from the host computer connected to a LAN. If NO in step ( 11 ), the flow advances to step ( 12 ) to determine whether a sleep command is received from the controller section  110  (CPU  114 ). This loop of processing is repeatedly executed until data or sleep command is received. 
     In this loop, if it is determined that a sleep command is received from the CPU  114 , power supply to all units connected to the bus  118  is stopped in step ( 13 ). At the same time, power to the engine section  120  is also stopped, and the sleep mode is set. 
     On the other hand, if YES in step ( 11 ), the flow advances to step ( 14 ) to acquire information in the status area of the RAM  116  (as described above, the RAM  116  receives power supply even in the sleep mode) and returns the information to the host computer (an ID for specifying the host computer is stored in the received data) as the data source. If the sleep state is set at that point of time, information representing the sleep state is sent to the host computer. 
     When the return processing of the status information is completed, the flow advances to step ( 15 ) to determine whether the apparatus main body is currently set in the sleep state. If NO, i.e., it is determined that the printing standby state is set, or the printing state is set on the basis of the printing data from the host computer, the flow advances to step ( 18 ) to interrupt the CPU  114 , thereby causing the CPU  114  to perform interrupt processing (receiving processing). 
     On the other hand, if YES in step ( 15 ), the flow advances to step ( 16 ) to determine whether the received data is a printing request command. If NO in step ( 16 ), it is determined that the apparatus requests printing during the sleep state. Therefore, this request is ignored, and the flow returns to step ( 11 ). 
     If YES in step ( 16 ), the flow advances to step ( 17 ) to start power supply to the controller section  110 , thereby canceling the sleep state. 
     With this operation, the CPU  114  of the controller section  110  starts processing based on the above-described flow chart in FIG.  3 . 
     The printing data output processing of the host computer on the LAN will be described below with reference to the flow chart in FIG.  5 . 
     A program based on the flow chart in FIG. 5 may be the OS or printer driver of the host computer, or may be executed using an application program. In this case, an example in which the program is adapted as a printer driver which operates on the host computer will be described. This program is stored in the memory  92  and executed by the CPU  91  (FIG.  9 ). 
     FIG. 5 is a flow chart showing an example of printing data output processing procedures in the printing apparatus according to the present invention. Numbers ( 21 ) to ( 27 ) denote steps. 
     In step ( 21 ), a predetermined command is generated to each printer connected to the LAN to obtain a printer status. 
     The flow advances to step ( 22 ) to determine whether a printer in the printing standby state is present. If YES in step ( 22 ), it is determined that the printer can immediately perform printing processing, so that printing data is output to the apparatus (step ( 27 )). If a plurality of printers are set in the printing standby state, the printing data is output to a printer which is detected to be in the printing standby state first. 
     On the other hand, if NO in step ( 22 ), the flow advances to step ( 23 ) to determine whether a printer in the sleep state is present. 
     If YES in step ( 23 ), a printing request command is generated to the printer, thereby canceling the sleep state (step ( 24 )) and outputting the printing data (step ( 25 )). If a plurality of printers are set in the printing sleep state, the printing data is output to a printer which is detected to be in the sleep statefirst. 
     If NO in step ( 23 ), i.e., if it is determined that all printers are set in the printing state (representing that the printing processing for printing data from another host computer is in progress), information representing that all the printers on the network are “BUSY” is output (step ( 26 )). The operator is notified at the host computer side that all the printers are set in the printing state and cannot be currently used. For example, a predetermined message is displayed on the display unit  95 . 
     As described above, according to this embodiment, in the sleep state, power supply to the engine section is stopped, and additionally, power supply to most units of the controller section  110  is also stopped. Therefore, the power consumption can be reduced as compared to the prior art. 
     In addition, as for the operator of the host computer, since a printer in the printing standby state is preferentially selected before a printer in the sleep state, the operation environment of the system as a whole can be improved, and at the same time, power can also be effectively used in the system as a whole. 
     &lt;Description of Second Embodiment&gt; 
     In the above embodiment, the CPU  114  of the controller section  110  on the printing apparatus side determines whether or not the sleep mode should be set, and actual setting and canceling of the sleep mode is performed by the IOP  111 . The host computer generates a printing request command to cancel the sleep mode. 
     However, the present invention is not limited to this. For example, setting of the sleep mode may also be designated by the host computer, or status information may be returned only when a status request command is generated. 
     In this case, if a host computer requests printing processing, and it is determined that two or more printers are in the printing standby state, except for one printer, all remaining printers can be set in the sleep state. 
     In addition, if one of a plurality of host computers serves as a printer server, and printing data generated by each host computer does not require immediate printing (a command representing non-urgency is added to the head of the data), the printing data can be output to only one printer. 
     In the above embodiment, if data is input to the interface section, information representing the sleep state is immediately transferred to the host computer. However, a control command for performing a similar operation as the conventional sleep state can also be used. The sleep state can be set on the printing apparatus side regardless of the control command. 
     &lt;Description of Third Embodiment&gt; 
     The third embodiment will be described below. 
     In the above embodiments, if a printing command is issued from an application operating on a host unit (host computer), printers in the printing standby state (printer which is in a non-printing state, and whose printer controller section and engine section are powered) is preferentially selected before printers in the sleep state. If printers in the printing standby state are present, one of them is automatically selected, and the printing data is sent to the selected printer. 
     However, in some cases, it is not preferable if a printer is automatically selected, and printing data is sent to the selected printer. 
     For example, if a large number of printers are connected to a network, and a selected printer is far from a host computer which sends printing data, the operator must attend to the printer which is located at a distant location to recover the printing output. 
     Therefore, it is preferable if an operator can select a printer. That is, if a plurality of printers in the same state are present, it is preferable if a printer can be freely selected therefrom. 
     In the third embodiment, the above object is realized. 
     FIG. 6 is a flow chart showing part of the operation of a printer driver operating on a host computer, which is related to this embodiment. This processing is started in accordance with a printing command from an operator. As a matter of course, this program is stored in a memory  92  in the host computer as shown in FIG.  9  and executed by a CPU  91 . 
     In step S 31 , it is determined whether the status is obtained for all the printers connected to the network through an I/F  96 . If NO in step S 31 , the flow advances to step S 32  to generate a status transmission request command to one printer, thereby obtaining the status of the printer. 
     Note that the printer in the third embodiment has the same arrangement as that described in the first embodiment. Therefore, even when predetermined data, e.g., command data for obtaining status information in this embodiment is sent to a printer, the printer in the sleep state is not set in the printing standby state. The obtained status information includes the printing standby state, the sleep state, and the printing state. 
     When the status is obtained for all the printers by repeatedly executing processing in steps S 31  and S 32 , the flow advances to step S 33 . 
     In step S 33 , it is determined whether the icons of all printers are displayed on a display  95 . If NO in step S 33 , the flow advances to step S 34  to display an icon according to the status. As for all the printers, icons each corresponding to the status of a corresponding printer are displayed. 
     FIG. 7 is a view showing an example in which a total of four printers are connected to the network. Reference numerals  70  to  73  denote printer icons. “PRINTER 1  (ID or name on the network)” indicated by the icon  70  represents that the printer is currently set in the sleep state. The icons  71  and  72  represent the printing standby state, and the icon  73  represents the printing state. As a result, the operator can easily grasp the current state of each printer at a glance. 
     As shown in FIG. 7, when the status is displayed for all the printers, the flow advances to step S 35  to wait until one of the printer icons is selected by a pointing device or the like constituting an input unit  93 . If one of the printer icons is selected, the flow advances to step S 36  to determine whether the selected printer icon represents the printing standby state. If YES in step S 36 , the flow advances to step S 37  to output the printing data to the selected printer. 
     If a printer icon which does not represent the printing standby state is selected, the flow advances to step S 38  to determine whether the printer status corresponding to the selected printer icon is the sleep state. If YES in step S 38 , the flow advances to step S 39  to output a printing request command (described in the first embodiment) to the printer, and the printing data is output in step S 40 . 
     If it is determined that the selected printer represents neither the printing standby state nor the sleep state, i.e., the printer is currently set in the printing state, the flow advances to step S 41  to display a message for informing that the selected printer cannot perform the printing operation. 
     As described above, according to the third embodiment of the present invention, when the host computer issues a printing command, the current status of each of a plurality of printers is visually indicated, and one of them is selected, thereby performing the printing operation in the printer desired by the operator. 
     If a large number of printers in the printing standby state are displayed, a pointing device or the like may be used to send a command for setting the printers in the sleep state. 
     &lt;Description of Fourth Embodiment&gt; 
     In the third embodiment, an example has been described in which all operable printers (printers at least whose main switches are in an ON state) on the network are displayed. That is, printers in the printing standby state and printers in the sleep state are simultaneously displayed together. Regardless of presence of printers in the printing standby state, a printer in the sleep state can be operated to perform the printing operation. From the viewpoint of a user interface, this method is excellent because the closest one of printers capable of printing can be selected. On the other hand, since a printer in the printing standby state is not always positively preferentially selected, the power consumption of the system as a whole cannot be suppressed. 
     In the fourth embodiment, when the printing operation is to be performed, an icon list of printers in the printing standby state is displayed, and a printer to which printing data is output is freely selected from these printers. If no printer in the printing standby state is present, a printer can be freely selected from printers in the sleep state. 
     FIG. 8 is a flow chart showing the operation processing of a printer driver on a host computer in a host unit of the fourth embodiment. The printer has the same arrangement as that of the first embodiment. Additionally, a program corresponding to this flow chart is stored in a memory  92  and executed by a CPU  91 . 
     In step S 51 , it is determined whether the status is obtained for all the printers connected to the network. If NO in step S 51 , the flow advances to step S 52  to generate a status transmission request command to one printer, thereby obtaining the status of the printer. 
     When the status is obtained for all the printers, the flow advances to step S 53  to determine whether a printer in the printing standby state is present. 
     If YES in step S 53 , an icon corresponding to the printer in the printing standby state is displayed on a display unit  95  of the host computer in steps S 54  and S 55 . When at least one printer is set in the printing standby state, the icons of printers in the sleep state are not displayed. 
     If NO in step S 53 , the flow advances to step S 56  to determine whether a printer in the sleep state is present. If YES in step S 56 , an icon corresponding to the printer in the sleep state is displayed in steps S 57  and S 58 . 
     In either case, if printer icons are displayed, the flow advances to step S 59  to select one of the displayed icons using a pointing device of an input unit  93 . 
     In step S 60 , the status of the printer corresponding to the selected icon is determined. If a printer in the sleep state is selected, the flow advances to step S 61  to output a printing request command to the printer, thereby setting the printer in the printing standby state. 
     In step S 62 , printing data is output to the printer, thereby ending this processing. 
     If no printer in the printing standby state and in the sleep state is present, a message for informing that the printing operation cannot be performed is displayed in step S 63 , thereby ending this processing. 
     As described above, according to the fourth embodiment, printers in the printing standby state are preferentially selected, and a desired printer can be selected from the printers in the printing standby state. Therefore, the power consumption of the system as a whole can be suppressed as compared to the third embodiment. 
     In the third embodiment, an error message is displayed when a printing command is generated to a printer in the printing state. In the fourth embodiment, an error message is displayed when no printer in the printing standby state and in the sleep state is present. 
     However, when a printing operation is to be performed through the network, the printing operation is performed through a printer server, as is well known, and the printing data is generally supplied to the printer server. Therefore, if a printer server is used, the printing data may be sent to the printer server. Even if the desired printer is set in the printing state, the printing data may be set in a printing queue. In this case, however, the operator must realize that the printing output is going to be obtained with a slight delay. 
     In the first to fourth embodiments, the host unit (host computer) directly outputs a status information transmission command to the printer. However, if a printer server is used, the command may be output to the printer server. Upon reception of the command, the printer server acquires the current status of the corresponding printer and informs the status to the inquiring host computer. 
     In the above embodiments, the interface section is incorporated in the printing apparatus. However, the present invention can also be applied to an interface section which can be externally expanded. 
     In a recent printing apparatus, particularly in a printing apparatus designed for use in a network environment, a plurality of interface circuits are often provided. In addition, to cope with a larger number of interfaces, some printing apparatuses have an expandable interface circuit. 
     As described above, when the interface circuit in the present invention is externally expanded, power savings control is enabled in various types of interfaces. The type of an interface can be changed in the future only by changing the expandable interface circuit applicable to the present invention. 
     In addition, in the above embodiments, a laser beam printer is exemplified as a printing apparatus. However, these embodiments can also be applied to another apparatus using an electrophotography system such as an LED printer, as a matter of course. Furthermore, the present invention can also be applied to, e.g., a wire-dot or thermal transfer system although no dramatic effect cannot be expected as for reduction in power consumption. The effect is increased especially in an office having relatively large power consumption. 
     The above embodiments refer to only the sleep state of the printing apparatus. However, the present invention can be applied to a host computer having the sleep state. If the present invention is applied to another network resource, lower power consumption control of the network as a whole can be performed. 
     If the present invention is applied to the host computer, the effect of reduction of power consumption in the host computer can be obtained. Additionally, when a computer load is used to manage the status information, an effect of dispersing the computer load can also be obtained. 
     Therefore, the present invention may be applied to a system constituted by a plurality of equipments or an apparatus constituted by one equipment. The present invention can also be applied to a system or apparatus to which a program is supplied, as a matter of course. 
     As has been described above, according to the above embodiments, although the arrangement of the apparatus is slightly complicated as compared to the prior art, power consumption in the sleep state can be reduced as compared to the prior art. In consideration of the network environment, when this control method is applied to other resources, the network resource can be efficiently utilized. 
     As described above, according to the first invention according to the present invention, the control means of the interface section controls power supply from the power supply to the controller section and the engine section on the basis of data received from the host unit to limit power supply to the controller section and the engine section in the sleep state except for power supply in the interface section, thereby further saving power. 
     According to the second invention, the control means controls power supply such that power supply from the power supply to the controller section is started upon reception of a predetermined command from the host unit, and power supply from the power to the controller section is stopped upon reception of a predetermined command from the controller section. In accordance with a command from the host unit, the state of the printing apparatus can be reversibly switched from the sleep state to the standby state or from the standby state to the sleep state. 
     According to the third invention, the informing means of the interface section informs the status of the printing apparatus main body to the host unit such that the host unit can properly determine the current printer status of the printing apparatus. 
     According to the fourth invention, the interface section communicates with the host unit through a network. Upon reception of a command from any one of the host units, power supply to the controller section and the engine section in the sleep state can be limited except for power supply in the interface section, thereby further saving power. 
     According to the fifth invention, in accordance with information from the interface section, the host unit preferentially selects a printing apparatus whose printing apparatus main body is set in the standby state before a printing apparatus in the sleep state, thereby determining a printing apparatus capable of performing printing processing as quickly as possible. 
     According to the sixth invention, when the host unit recognizes that a plurality of printing apparatuses whose printing apparatus main bodies are set in the standby state are present, the host unit sends a command for setting one of the printing apparatuses in the sleep state to the interface section. With this operation, regardless of changes in status of each printing apparatus, a printing apparatus capable of performing printing processing can be determined as quickly as possible while printing apparatuses not subjected to printing are set in the sleep state. 
     According to the seventh invention, the interface section can be freely attached/detached to/from the printing apparatus main body, thereby coping with expansion or modification of the interface section. 
     According to the eighth invention, the interface section can be externally connected through the external interface port of the printing apparatus main body, thereby externally expanding the function of the interface section to a conventional printing apparatus. 
     Therefore, power supply to the controller section and the printer engine section, both of which have a large power loss, is controlled while the printer apparatus itself further reduces the power consumption in the sleep state, and at the same time, the communication state with the host unit can be ensured. 
     As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.