JPS59140554A - Electronic device - Google Patents

Abstract

PURPOSE:To make a hard logic for comparing work unnecessary by using an incorporated microcomputer to perform A/D conversion in an electronic device where the microcomputer is mounted. CONSTITUTION:A read-only memory 23 where a subroutine for the A/D conversion is written is prepared, and a microcomputer 21 is used to compare an analog signal 31 supplied to an input terminal 29 of a comparator 28 with a D/A conversion output 32 outputted from a D/A converter 25. The comparison result is transmitted to a data bus 22, and thus, the hard logic for comparing work is unnecessary.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electronic device equipped with a microcomputer, such as an electronic copying machine or a facsimile machine.

``Prior Art'' With the increasing sophistication of control of electronic devices and the spread of semiconductor devices, many electronic devices equipped with microcomputers have appeared. Such devices use digital signals to perform various controls and store data. Therefore, it is necessary to convert analog signals into digital signals in advance.

The basic circuit that converts the Noah's signal into a multivalued digital signal is a circuit in which multiple comparators are connected in parallel. , and then compare the analog signals to obtain a digital signal. However, with this circuit, if you try to convert an analog signal to a digital signal with sufficient resolution, it becomes a large and complex configuration, making it difficult to realize. Met.

On the other hand, as another circuit that converts analog signals into digital signals, there is an analog-digital converter (hereinafter referred to as A/
D converter) is sometimes used. Among these converters, there is a converter called a successive approximation type or a comparison follow-up type as a relatively high-speed converter that is usually used in electronic devices equipped with a microcomputer. These −
The S1 converter has a built-in digital-to-analog converter circuit (hereinafter referred to as a D/A converter circuit), and the reference voltage generated from this and the analog signal are compared by the converter. Perform encoding.

Figure 1 shows the successive approximation type A/D'D amplifier.
It represents ta. This inverter is configured to sequentially output voltages for comparison by a /A conversion circuit 12 connected to a reference voltage circuit 11. This comparison voltage is compared with the ablog signal input to the comparison terminal 15 of the comparator 14. The programmer 16 performs the comparison operation using a clock signal 18 supplied from a clock generator 17. In other words, the grammar 16 reads the MSB (highest 1~) of the output register 19.
'1'', and in this state the D/A conversion circuit 12
A voltage F S / 2 of 1/2 of the Nord scale is output from the voltage F S /2.

When the analog signal input to the comparison terminal 15 is higher than this comparison voltage, the second pin] of the output register 19 is set to 1'', and the 1]/A conversion circuit 12 outputs 3 F S / 4. voltages are output and compared.

On the other hand, in the first stage of comparison, if the voltage value of the ant 1 signal is lower than FS/2, the first signal II
II is reset, and the FS/
4 voltages are output and compared. In this way, the analog signals are compared until the LSBut low order bits are determined.

The comparison result is the converted digital signal. On the other hand, a comparison-following type A/I'-E converter constantly compares the analog signal with the output of the D/A converter circuit, and when the analog signal becomes larger, the up count is increased, and when the analog signal becomes smaller, the output is increased. Town Calendar 1~ is performed, and the old value of the counter at this time is used as the converted digital signal.

In this way, any A/D with built-in /A conversion conversion
Since the converter also performs comparison work using a comparator, dedicated hard logic is required to execute this. This hard logic must be manufactured with consideration given to the high speed and resolution of Al1) conversion, which has caused the electronic device itself to be expensive. In comparatively low-cost electronic devices, such A/D converters were commonly used.

[Object of the Invention] In view of the above-mentioned circumstances, an object of the present invention is to provide an electronic device that can eliminate the need for hard logic for performing comparison work using a comparator.

[Means for achieving the object] In the present invention, a read-only memory in which a subroutine for A/D conversion is written is prepared, a microcomputer installed in an electronic device is used to perform the comparison operation, and the above-mentioned Achieve your purpose.

The present invention will be described in detail below with reference to Examples.

[Embodiment] FIG. 2 shows the main parts of the electronic device of this embodiment. This device is equipped with a central processing unit (CPU) 21 to control each part. Central processing unit @21
Inside are B register, C register, D register and
It is equipped with 4 registers. The central processing unit 21 connects via a data bus 22 a read-only memory 23, a random access memory 24. -1.2
6-2, . . . are connected. In the read-only memory 23, a subroutine for performing Δ/D conversion is written in machine language. 1st I10 boat 2
6-1 is a port used for Δ/D conversion, and is connected to a comparator 28 via a level conversion circuit 27.

The analog signal 31 supplied to the input)j terminal 29 of the comparator 28 is compared with the 1]/A output 32 output from the D/A converter 25, and the result is sent to the data bus 22. Other I10 boats 26-2...
... are connected to other input/output devices (not shown) and are used for other operations of this electronic device.

Next, the operation when this electronic device performs A/D conversion using the successive approximation method will be explained with reference to FIG.
6 or Sera 1. Since this device processes data using 8 hits, a value of 2 to the 8th power is set as the -nor scale. Further, the C register is set with η number candy ε3 representing the number of data processing, and the 1] register is set with a number O.

Next, the first data processing starts. The content of this B register is multiplied by 1/2, and the value 12F3 becomes 13
This value 128 is also stored in the 1, 1 register. [) The contents of the register are D/
The A converter 25 outputs the [ )/A output 32 to the comparator 28 . The 21 comparator 28 compares this value of 1/2 of the full scale with the value of the 21st full scale signal 31, and reads the result into the X register. At this time, the analog signal 1 is larger than the D/A output 32 (the bias is x-1, otherwise it is X-0.
1 Lee 1, that is, if X≠O, then the contents of the C register are 1 (subtracted), and the second data processing is h1. If so, the size is X≠0
If you pull (, the content of the B register is subtracted from the C register and the result is stored in the C register. In this case, the C register is set to O again. After this, the content of the C register becomes 1 ( ] and the second data processing is performed.

The second data processing is basically the same as the first data processing. However, the B register is set to the number 64, and the C register is set to 192 (3/4 of full scale) in the former case and 64 (1/4 of full scale) in the latter case.
) is set.

After data processing is performed up to eight times in the same manner, the contents of the C register become O, and all A/D conversion operations are completed. The A/D converted data is directly sent to the central processing unit 2.
1 or stored in random address memory 24.

Although successive approximation type A/D conversion has been described above, by changing the program written to the read-only memory 23, it is also possible to perform A/D conversion using the Haku method. Note that it is practical to combine the read-only memory, D/A comparator, comparator, and I10 board used for A/D conversion into one package so that they can be removed as necessary. ” - extremely useful.

[Effects of the Invention] As described above, according to the present invention, A/D conversion is performed using a microcomputer built into an electronic device.
The number of circuit components for conversion can be reduced and the reliability of circuit operation can be improved.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional successive approximation type A/D inverter, Fig. 2 is a block diagram showing the main parts of an electronic device according to an embodiment of the present invention, and Fig. 3 is a block diagram of this electronic device. It is a flow chart for explaining operation of A/D conversion. 21...Central processing unit, 23...Read-only memory, 25...
...D/A converter, 28...Comparator, 31...Analog signal. 8-

Claims (1)

[Claims] A central processing unit that performs various controls within the device, and a read/write unit that contains subroutines for A/D conversion.
a D y'A converter that creates an analog signal for comparison in accordance with the execution of the 1J blue routine, such as a memory;
It is characterized by comprising a comparator that compares an analog signal received from the outside with the output of the D/A converter, and enables execution of a subroutine for converting the analog signal into a digital signal. electronic equipment.