ADC0804LCN National Semiconductor, ADC0804LCN Datasheet - Page 27

• Manufacturer Part Number: ADC0804LCN
• Description: IC, ADC, 8BIT, 9708SPS, DIP-20
• Manufacturer: National Semiconductor

Specifications of ADC0804LCN

• Resolution (bits): 8bit
• Sampling Rate: 9.708kSPS
• Input Channel Type: Differential
• Data Interface: CMOS, Parallel, TTL
• Supply Current: 1.9mA
• Digital Ic Case Style: DIP
• No. Of Pins: 20
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Functional Description
Note 18: The stack pointer must be dimensioned because a RST 7 instruction pushes the PC onto the stack.
Note 19: 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.
4.1.1 Sample 8080A CPU Interfacing Circuitry and
Program
The following sample program and associated hardware
shown in Figure 12 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 con-
verter.
SAMPLE PROGRAM FOR Figure 12 ADC0801–INS8080A CPU INTERFACE
(Continued)
27
It is important to note that in systems where the A/D con-
verter 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.
4.1.2 INS8048 Interface
The INS8048 interface technique with the ADC0801 series
(see Figure 13 ) 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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