ADC0809 and PC bus interface circuit

The ADC0809 is an 8-bit successive approximation A/D converter with 8-channel analog switches. The 8-channel analog switch of ADC0809 can realize
8-select-1 operation, address latch and decoder channel selection signals ADDA, ADDB, ADDC. Used to select one of the 8 input channels
, the address latch enable signal ALE can connect the input channels selected by ADDA, ADDB, and ADDC to the A/D converter.
  The 8-bit successive approximation state D converter
can convert the input analog signal
into an 8-bit binary representation, and the conversion
result is stored in the three-state latch output buffer
. The positive pulse signal SD\RT
can cause the A/D converter to start conversion.
After about 100tjtS, the conversion is completed
. After the conversion is completed. The EOC signal changes from low
level to high level. Notify
the CPU to read data.
    The three-state latch output buffer is used
to store the conversion result when the output enable
signal OE is high level. The 8-bit conversion result is output by DO-D7. When OE is low level, the data output line DO-D7 is in a high-impedance state.
    Since the ADC0809 has a three-state latched output buffer, it can be connected directly to the system bus. In order to facilitate or simplify the interface circuit
design, the interface with the system is usually implemented through a universal parallel interface chip. The circuit shown in the figure is a circuit in which ADC0809 is connected to a PC through the programmable parallel interface
chip 8255A .