Abstract:
An electronic apparatus with an interchangeable peripheral device, in which, when the interchangeable peripheral device is changed, a corresponding signal is sent to a microprocessor to shift it to a halt state, which is released by the termination of the signal, thereby preventing the erroneous operation of the microprocessor.

Description:
This application is a continuation of application Ser. No. 08/062,153, filed May 17, 1993, now abandoned, which is a continuation of application Ser. No. 07/383,275, filed Jul. 19, 1989, now abandoned, which is a continuation of application Ser. No. 07/099,615, filed Sep. 22, 1987, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electronic apparatus, and, more particularly to an apparatus equipped with a microprocessor having a halt function and an interruption function, and an interchangeable peripheral device connectable with the microprocessor through a connector or the like. 
     2. Related Background Art 
     In the conventional apparatus of this kind, the interchange of a peripheral device connected to the microprocessor (hereinafter called CPU) during the function thereof induces runaway or erroneous operations of the CPU. For this reason such interchange is generally effected after the power supply is cut off. If the power supply is not cut off, the interchange may be effected while the CPU does not make access to the peripheral device to be interchanged. However, in order to prevent erroneous operations of the CPU caused by the contact noises of the connector or the like at the interchange, a buffer circuit is inserted between the bus line of the CPU and the peripheral device. Thus, the connector and the bus line are electrically insulated by the buffer circuit before the peripheral device is mechanically removed from the connector, and the insulation is removed after the interchange. However, the former method is inconvenient as the power supply has to be cut off at each interchange, while the latter method is associated with an increased cost due to the presence of the buffer circuit. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an electronic apparatus having a peripheral device connectable to a processor through a bus line, in which the function of the processor is interrupted when the peripheral device is detached from the bus line. 
     Another object of the present invention is to provide an electronic apparatus involving an interchangeable peripheral device, comprising a processor (hereinafter called a CPU ) having a halt function; an interchangeable peripheral device connected through a connector to the bus line of the CPU; device interchange signal generating means for generating, at the interchange of the device, a signal indicating that the interchange of the device is in progress; and device interchange signal detecting means for causing the CPU to detect the signal; wherein the CPU is shifted to a halt state in response to the detection of the device interchange signal by the CPU at the interchange of the device, and the halt state is cancelled at the termination of the signal. 
     The foregoing and still other objects of the present invention, and the advantages thereof, will become fully apparent from the following description of the embodiments of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of an embodiment of the present invention; 
     FIG. 2 is a detailed view of a part directly related to the present invention in FIG. 1; and 
     FIG. 3 is a chart showing the function of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now the present invention will be clarified in detail by an embodiment thereof consisting of an electronic typewriter equipped with a dot printer. FIG. 1 is a block diagram of the embodiment. 
     A microprocessor 1 (hereinafter called a CPU) reads program instructions from a ROM to be explained later, executes processes necessary for typewriting and controls a keyboard, a printer, a display unit etc. The CPU is provided with an interruption port (IRQ port) and executes an interruption process when the port is activated. Also the CPU is capable of a halt function and has a halt port which is normally maintained at a logic &#34;L&#34; level. When the port is shifted to the &#34;H&#34; level, the CPU does not read a next instruction after the completion of an instruction currently in execution, and enters a halt state in which the function is temporarily suspended. When the port is shifted to the L-level again, it restarts the reading and execution of the instructions. 
     A HALT/IRQ controller 2 is used for the control at the interchange of a peripheral device (CGROM 5 to be explained later) of the typewriter. 
     A connector 3 is used for connecting the CGOM 5 to be explained later with a bus line and a control line of the CPU 1. 
     A door switch 4 is used for generating a signal indicating that the interchange of the CGROM 5 is in progress. 
     A character generator ROM (CGROM) 5 interchangeably connected to the connector 4 is prepared in different fonts and enables typewriting in different styles when interchanged. 
     A RAM 6 is used for temporarily storing results of calculation and various data during the execution of instructions of the CPU 1. 
     A read-only memory (ROM) 7 stores a program for the CPU 1. 
     A display unit 8 displays data entered from a keyboard to be explained later, and information necessary for typewriting. 
     An input/output controller 9 is used for transmitting the signal from the keyboard to the CPU 1 or transmitting the control output signals to a printer to be explained later. 
     A printer 10 is used for printing the dot patterns read by the CPU from the CGROM 5 according to the key data entered from the keyboard. 
     A keyboard 11 constitutes input means for entering various data for printing or editing texts. 
     A bus line S1 is provided for data transfer and control of various parts to be executed by the CPU 1. 
     A control line S2 is used for controlling the halt function, to be explained later, of the CPU 1. 
     A control line S3 is used for controlling the interruption function, to be explained later, of the CPU 1. 
     FIG. 2 is a detailed view of a part of the present embodiment directly related to the present invention. 
     Output registers 2.1, 2.5 respectively supply signal lines S5, S6 with signals for controlling halt and interruption enable ports of the CPU 1. 
     The halt function or the interruption function of the CPU is enabled through an AND gate 2.3 or 2.7 when the output of the output register is in a logic level &#34;1&#34; and the signal line S4 (device interchange signal ) is at the logic level &#34;1&#34;. 
     An input port 2.2 or 2.6 is enabled when the output of the output register 2.1 or 2.5 is at the logic level &#34;0&#34; whereby the CPU can detect the logic level of the signal line S4. 
     A cover (lid) 4.1, a pull-up resistor 4.2 and a door switch 4 which is closed or opened respectively when the cover is opened or closed, constitute a mechanism for generating the device interchange signal. 
     Now there will be given an explanation of the function of the present invention, while making reference to FIGS. 1 and 2. 
     In the normal function of the present system as a typewriter, the CPU detects the key information from the keyboard 11 through the input/output controller 9, and accordingly executes the display on the display unit, or temporary storage in the RAM, or reading of dot patterns from the CGROM 5 and supply thereof to the printer 10. Different fonts such as courier, Italic and pica can be obtained by changing the CGROM 5. 
     In the above-explained function of the present system as a typewriter, the output register A 2.1 is set at &#34;0&#34; while the output register B 2.5 is set at &#34;1&#34; so that the signal line S2 is at a level &#34;0&#34; even when the signal line S4 is at a level &#34;0&#34;, whereby the halt function of the CPU 1 is inhibited while the interruption function is enabled. Also the input port A 2.2 is enabled while the input port B 2.6 is inhibited. Furthermore, in the normal operation with the cover closed, the door switch 4 is opened whereby the logic level of the device interchange signal on the line S4 is maintained at &#34;1&#34; by the pull-up resistor 4.2 to maintain the interruption control line S3 at &#34;0&#34;  even when the signal line S6 is at &#34;1&#34;. Therefore the interruption procedure is not started. 
     FIG. 3 shows the procedure of interchanging the CGROM 5 for varying the typewriting font. As the cover 4.1 is opened for the interchange, the door switch 4 is closed to shift the line S4 to the logic level &#34;0&#34; and the line S3 to the level &#34;1&#34; thereby requesting an interruption procedure of the CPU 1. Thus, the CPU 1 jumps to an interruption routine (CGROM interchange routine). At first, in order to prevent multiple interruptions caused by the chattering of the door switch, the output register B 2.5 is shifted from &#34;1&#34; to &#34;0&#34;. Then the CPU executes a pre-halt process, such as the lifting of the printing head or the stopping of the driving motor if a printing operation is in progress, or the protection of the input text if a text entry is in progress. Then the CPU passes a timer routine of a predetermined period to terminate the chattering of the door switch 4, then it confirms that the signal line S4 is at a logic level &#34;0&#34; and shifts the output register A 2.1 from &#34;0&#34; to &#34;1&#34; thereby enabling the halt function of the CPU. Since the signal line S4 is already at the logic level &#34;0&#34;, the CPU 1 immediately enters the halt state through the AND gate 2.3 and the signal line S2. The CGROM 5 is interchanged in such halt state of the CPU 1. The time required from the closing of the door switch 4 to the start of the halt state of the CPU 1 is shorter than the period from the completion of the opening of the cover 4.1 to the moment when the CGROM 5 is touched by the operator. After the interchange of the CGROM 5, the cover 4.1 is closed to open the door switch 4 whereby the signal line is shifted from the logic level &#34;0&#34; to &#34;1&#34;. Thus the signal line S2 is shifted from the logic level &#34;1&#34; to &#34;0&#34; to terminate the halt state of the CPU 1. In order to prevent the repeated halt state by the chattering of the door switch 4, the CPU 1 shifts the output register A 2.1 from &#34;1&#34; to &#34;0&#34;, thereby inhibiting the halt function, and executes a post-halt process for returning to the typewriting function. Then the CPU passes a timer routine for terminating the chattering of the door switch 4, then confirms through the input port A 2.2 that the signal line S4 is at the logic level &#34;1&#34;, and shifts the register B 2.5 from &#34;0&#34;  to &#34;1&#34; thereby enabling the interruption function and terminating the interruption routine. In this state the interruption is not started again since the signal line S4 is at the level &#34;1&#34;. The interchange of the CGROM 5 is thus completed, and the normal typewriting operation is restored. 
     In the foregoing explanation, the present invention has been explained by an embodiment in which the electronic apparatus is an electronic typewriter equipped with a dot printer, and the peripheral device to be interchanged is a CGROM, but the present invention is applicable to any combination of an electronic apparatus having a CPU and an interchangeable peripheral device controlled or operated by the bus lines of the CPU, such as a combination of a Japanese word processor and a CGROM, a dictionary ROM or a text RAM, or a combination of a personal computer and a language ROM, a game ROM or a sub-CPU. 
     A port A in FIG. 2 may be regarded as an input port instead of the halt port by switching the output register A 2.1 and a port B may be used as an input port instead of the interruption function. Therefore there may be employed, instead of the CPU 1 in FIG. 2, a CPU in which halt and interruption controls are combined. 
     As explained in the foregoing, it has been rendered possible to interchange the CGROM of a typewriter without interrupting the power supply and without the use of a buffer circuit, through suitable use of the interruption function and the halt function of the CPU.