|ADC0801||8-Bit µP Compatible A/D Converters|
|ADC0801 Datasheet PDF : 48 Pages |
ADC0803, ADC0804, ADC0805
SNOSBI1B – NOVEMBER 2009 – REVISED FEBRUARY 2013
SAMPLE PROGRAM FOR Figure 56 ADC0801–INS8080A CPU INTERFACE
Note: The stack pointer must be dimensioned because a RST 7 instruction pushes the PC onto the stack.
Note: All address used were arbitrarily chosen.
The standard control bus signals of the 8080 CS, RD and WR) can be directly wired to the digital control inputs
of the A/D and the bus timing requirements are met to allow both starting the converter and outputting the data
onto the data bus. A bus driver should be used for larger microprocessor systems where the data bus leaves the
PC board and/or must drive capacitive loads larger than 100 pF.
Sample 8080A CPU Interfacing Circuitry and Program
The following sample program and associated hardware shown in Figure 56 may be used to input data from the
converter to the INS8080A CPU chip set (comprised of the INS8080A microprocessor, the INS8228 system
controller and the INS8224 clock generator). For simplicity, the A/D is controlled as an I/O device, specifically an
8-bit bi-directional port located at an arbitrarily chosen port address, E0. The TRI-STATE output capability of the
A/D eliminates the need for a peripheral interface device, however address decoding is still required to generate
the appropriate CS for the converter.
It is important to note that in systems where the A/D converter is 1-of-8 or less I/O mapped devices, no address
decoding circuitry is necessary. Each of the 8 address bits (A0 to A7) can be directly used as CS inputs — one
for each I/O device.
The INS8048 interface technique with the ADC0801 series (see Figure 57) is simpler than the 8080A CPU
interface. There are 24 I/O lines and three test input lines in the 8048. With these extra I/O lines available, one of
the I/O lines (bit 0 of port 1) is used as the chip select signal to the A/D, thus eliminating the use of an external
address decoder. Bus control signals RD, WR and INT of the 8048 are tied directly to the A/D. The 16 converted
data words are stored at on-chip RAM locations from 20 to 2F (Hex). The RD and WR signals are generated by
reading from and writing into a dummy address, respectively. A sample interface program is shown below.
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