JPH11161248A - Microcomputer for display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To continuously display contents of a display RAM from those at the time of power failure or instantaneous power outage when the power source is turned on again after its service is interrupted or instantaneously cut off. SOLUTION: When an overflow signal is generated from a timer circuit 9, contents of a display RAM 2 are written in a flash memory 7 via a control circuit 8 and a flag 10 is set to a logical value '1'. When a power source is turned on again after its service is interrupted or instantaneously cut off and its voltage passes through a low voltage detection voltage, the contents of the flash memory 7 is written in the display RAM 2 via the control circuit 8 if the flag 10 is a logical value '1'.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a display microcomputer for displaying a predetermined character on a display panel (such as a liquid crystal panel).

[0002]

2. Description of the Related Art Characters (characters, numbers, pictures, etc.) displayed on a liquid crystal panel are a group of dots, and dot data corresponding to a display character for one screen of the liquid crystal panel is stored in a display RAM (static RAM structure). ). For example, it is assumed that one dot data instructs lighting when the logical value is “1” and turns off when the logical value is “0”. Note that the address of the display RAM corresponds to the display position of the liquid crystal panel on a one-to-one basis. That is, when a character is displayed at the position A of the liquid crystal panel, the position A of the liquid crystal panel is displayed.
Is designated, and the dot data is read out. Then, based on the dot data, the common electrode and the segment electrode constituting the liquid crystal panel are selectively driven, and the liquid crystal display is performed. The display driving means for liquid crystal display is integrated on a microcomputer chip.

[0003]

However, when the power supply of the liquid crystal display device incorporating the microcomputer is subjected to a power failure or an instantaneous power failure against a user's intention due to some factor, the display RAM has a volatile characteristic. , All the contents of the display RAM at that time are cleared.
Therefore, when the power is restored, the LCD display should be continued from the contents at the time of power failure or momentary power failure.
Actually, the liquid crystal display must be started from the initial state, and there is a problem that the contents of the display RAM from the initial state to the power failure or the instantaneous power failure are wasted.

In view of the above, the present invention provides a display for displaying a liquid crystal display which can be continued from the content at the time of the power failure or instantaneous power failure when the power source is restored after the power failure or instantaneous power failure contrary to the intention of the user. It is intended to provide a microcomputer.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and character data for a character to be displayed on a display panel is stored in a pair at a display position of the display panel. A display RAM to be written to an address corresponding to 1; a latch circuit for latching read data of the display RAM; and a drive circuit for displaying a character corresponding to the latch data of the latch circuit on the display panel. A display microcomputer having a characteristic that data can be collectively or partially erased, data can be written and read, and an address corresponding to the display RAM on a one-to-one basis. A memory, and a control circuit for writing the same content as the display RAM to the nonvolatile memory. That.

The control circuit has a built-in counting circuit, and writes the contents of the display RAM to the nonvolatile memory each time the counting circuit counts a predetermined time. The time counted by the counting circuit is
The content of the display RAM is shorter than the shortest time in which the content must be changed.

The control circuit displays the contents of the nonvolatile memory when the power supply voltage of the display microcomputer falls below the data holding voltage of the display RAM and thereafter rises above the data holding voltage of the display RAM. For R
AM is written. The nonvolatile memory is a flash memory.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be specifically described with reference to the drawings. FIG. 1 is a block diagram showing a display microcomputer of the present invention. In FIG. 1, (1) is a liquid crystal panel in which m common electrodes and n segment electrodes are arranged in a matrix, and a predetermined character is displayed by turning on or off a dot at an intersection of the common electrode and the segment electrode. Things. Reference numeral (2) denotes a display RAM in which display data, ie, dot data, constituting a character for one screen of the liquid crystal panel (1) is written to a display position of the liquid crystal panel (1) at an address corresponding to one to one. It is. The dot data written to and read from the display RAM (2) instructs lighting when the logical value is "1" and turns off when the logical value is "0", and is equivalent to one screen of the liquid crystal panel (1). When all or part of the display content has to be changed, only the changed content is rewritten. The reading speed of the dot data from the display RAM (2) is set so that the frequency until the liquid crystal display for one screen of the liquid crystal panel (1) is completed becomes a predetermined alternating frequency. . Reference numeral (3) denotes a parallel-serial conversion circuit for converting dot data read from the display RAM (2) in units of words (in units of one byte when one word is 8 bits) from a parallel state to a serial state. . Reference numeral (4) denotes an n-bit shift register which sequentially shifts serial data output from the parallel-serial conversion circuit (3) in synchronization with the dot clock DCLK, and outputs n-dot data for one row of the liquid crystal panel (1). Is held. (5) is an n-bit latch circuit for latching the n-bit dot data held in the shift register (4) in synchronization with the latch clock LCLK. Reference numeral (6) denotes a drive circuit for sequentially selecting a common electrode for each row of the liquid crystal panel (1) and selecting a segment electrode according to latch data of the latch circuit (5). That is, the drive circuit (6) turns on the intersection of the selected common electrode and segment electrode. When this operation is repeated m times, the character display for one screen of the liquid crystal panel (1) is completed.

A flash memory (non-volatile memory) (7) has a characteristic that all or a part of data can be electrically erased and data can be written and read. Flash memory (7) has RA for display
M (2) has the same number of addresses, and the address of the flash memory (7) is equal to the address of the display RAM (2) by one.
Corresponds to one. (8) is a control circuit, and a display RA
It controls the writing operation and the reading operation of the dot data with respect to the M (2) and the flash memory (7). The control circuit (8) has a built-in timer circuit (9). That is, every time the timer circuit (9) outputs the overflow signal, the control circuit (8) reads the contents of the display RAM (2) and writes the read contents to the flash memory (7). The timer circuit (9) outputs an overflow signal and returns to an initial value, and repeats counting. As shown in FIG. 2, the time T 'from the start of counting by the timer circuit (9) to the output of the overflow signal is the shortest time T required to change the display character of the liquid crystal panel (1). Set shorter. For example,
Consider a case in which the power supply stops or instantaneously stops at time t1, and returns at time t2. In this case, the contents of the display RAM (2) are rewritten at time t0, and the contents of the flash memory (7) are also rewritten to the contents of the display RAM (2) at this time. Therefore, if the contents of the flash memory (7) are written into the display RAM (2) after time t2, the liquid crystal display can be continued from the contents at the time of the power failure or momentary power failure. For example, it is suitable for use in an apparatus in which the liquid crystal display changes periodically. The control circuit (8) also has a built-in non-volatile flag (10) which becomes a logical value "1" when the writing of data in the display RAM (2) to the flash memory (7) is completed.

The write operation of the flash memory (7) will be described below with reference to FIG. First, the timer circuit (9) starts counting (step 1), and determines whether there is an overflow signal from the timer circuit (9) (step 2). If there is no overflow signal, the determination of the presence or absence of the overflow signal is repeated (step 2N).
O) If there is an overflow signal, the signal acts as a timer interrupt request signal. That is, the main routine program is interrupted, the ROM address data at this time is saved, the ROM address is jumped, and the process shifts to execution of a subroutine program responding to the timer interrupt request (step 2 YES).
Specifically, the contents of the display RAM (2) are read into the control circuit (8) (Step 3), and then the contents of the display RAM (2) read into the control circuit (8) are stored in the flash memory (7). (Step 4). That is, the contents of the display RAM (2) and the flash memory (7) are the same. When the writing to the flash memory (7) is completed, the logical value “1” is set to the flag (10),
A series of subroutine programs ends (step 5). At this time, the timer circuit (8) starts the counting operation again, while the save address of the ROM is designated, and the process returns to the main routine program processing. Thereafter, each time the timer circuit (9) outputs an overflow signal, the subroutine program processing is repeated.

Next, the read operation of the flash memory (7) will be described with reference to FIG. First, during the execution of the main routine program, if the power supply voltage fails or momentarily stops and then recovers, the contents of the display RAM (2) are restored when the power supply voltage passes the low voltage detection voltage during the recovery process. An interrupt request for the contents before the stop is generated. In accordance with the interrupt request, the main routine program processing is interrupted, the ROM address data at this time is saved, the ROM address is jumped, and the process proceeds to the subroutine program processing. That is, it is determined whether or not the flag (10) has the logical value "1" (step 1). If the flag (10) has the logical value "0", it is determined that the power supply has stopped or the power supply has stopped momentarily before the output of the overflow signal from the timer circuit (9). Not performed (step 1 NO). On the other hand, when the flag (10) is the logical value "1" (step 1YE
S), the contents of the flash memory (7) are controlled by the control circuit (8)
(Step 2), and then the content of the flash memory (7) read into the control circuit (8) is displayed on the display RA.
M (2) is written, and a series of subroutine program processing ends (step 3). Then, the save address of the ROM is designated, and the program returns to the main routine program.

As described above, even when the power supply is interrupted or instantaneously shuts down and thereafter the power supply is restored, the display RAM
The content of (2) can be continuously displayed from the content at the time of the power failure or momentary power failure.

[0013]

According to the present invention, even if the power supply is interrupted or instantaneously stopped, and then the power supply is restored, the display R
There is an advantage that the contents of the AM can be continuously displayed from the contents at the time of the power failure or momentary power failure.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a display microcomputer of the present invention.

FIG. 2 is a time chart showing the operation of FIG.

FIG. 3 is a flowchart showing a write operation of the flash memory of FIG. 1;

FIG. 4 is a flowchart showing a read operation of the flash memory of FIG. 1;

[Explanation of symbols]

 (1) Liquid crystal panel (2) Display RAM (5) Latch circuit (6) Drive circuit (7) Flash memory (8) Control circuit

Claims (5)

[Claims] 1. A display RAM in which character data for a character to be displayed on a display panel is written at an address corresponding to a display position of the display panel on a one-to-one basis.
A display microcomputer comprising: a latch circuit for latching read data of the display RAM; and a drive circuit for displaying a character corresponding to the latch data of the latch circuit on the display panel. A non-volatile memory that has a characteristic of enabling an electrical erasure and writing and reading data, and has an address corresponding to the display RAM in a one-to-one correspondence; A display microcomputer, comprising: a control circuit for writing data to a volatile memory. 2. The control circuit according to claim 1, wherein the control circuit has a built-in counting circuit, and writes the contents of the display RAM to the nonvolatile memory each time the counting circuit counts a predetermined time. Item 2. The display microcomputer according to Item 1. 3. The display microcomputer according to claim 2, wherein the time counted by the counting circuit is shorter than the shortest time in which the contents of the display RAM must be changed. 4. The control circuit according to claim 1, wherein when the power supply voltage of the display microcomputer falls below the data holding voltage of the display RAM and thereafter rises above the data holding voltage of the display RAM, the contents of the nonvolatile memory are read. 2. The display microcomputer according to claim 1, wherein said display microcomputer is written in said display RAM. 5. The display microcomputer according to claim 1, wherein said nonvolatile memory is a flash memory.