Data acquisition system circuit

Converter and data sampling: Figure 27-47 is the 12-bit A/D converter AD574 and 8031 ​​interface circuit. The measured parameters
are sent to the input end of the sample/hold device after being gated by the multi-way switch CD4051. Which two channels are selected
is controlled by the selection control terminals c, B, A and the storage terminal INH of the multi-channel switch. The working state of the sample/hold device is controlled by the state of the conversion end flag STS of the /VD converter. When
the A/D conversion is in progress, the STS output is high level . After inversion, it becomes low level and is sent to the S/H sealing logic control slope end (Logic), so that
S/H is in the hold state. A/:D conversion can be started. The converted digital quantity is read into the CPU register through the 8031 ​​to the data bus in two times
.
    After the conversion is completed, STS changes from high level to low level, and then becomes high level , thus making S/H enter the sampling state.
    3) Keyboard/display interface circuit: In order to enable the operator to grasp the temperature changes of each furnace at any time, a 4-digit LED display is designed
. Assume that the display buffer units are 28H and 29H. The 2nd to 4th bits indicate the channel number. The 2nd to 4th bits are used to display the temperature. The maximum is 999°C. According to
the needs of the system. The display method is designed in two ways: A. Automatic cycle display. In the invitation mode, the computer can automatically
display the sampled temperatures of No. 1 to No. 8 annealing furnaces in sequence; B. Fixed-point display, that is, the operator can You can check the temperature of a certain annealing furnace at any time,
and the two display modes can be switched at will.