ADC0804LCN National Semiconductor, ADC0804LCN Datasheet - Page 24

• 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
For a higher speed test system, or to obtain plotted data, a
(Continued)
digital-to-analog converter is needed for the test set-up. An
accurate 10-bit DAC can serve as the precision voltage
source for the A/D. Errors of the A/D under test can be
expressed as either analog voltages or differences in 2
digital words.
A basic A/D tester that uses a DAC and provides the error as
an analog output voltage is shown in Figure 8 . The 2 op
amps can be eliminated if a lab DVM with a numerical
subtraction feature is available to read the difference volt-
age, “A–C”, directly. The analog input voltage can be sup-
plied by a low frequency ramp generator and an X-Y plotter
can be used to provide analog error (Y axis) versus analog
input (X axis).
For operation with a microprocessor or a computer-based
test system, it is more convenient to present the errors
digitally. This can be done with the circuit of Figure 11 , where
the output code transitions can be detected as the 10-bit
DAC is incremented. This provides
1
⁄
LSB steps for the 8-bit
4
A/D under test. If the results of this test are automatically
plotted with the analog input on the X axis and the error (in
LSB’s) as the Y axis, a useful transfer function of the A/D
under test results. For acceptance testing, the plot is not
necessary and the testing speed can be increased by estab-
lishing internal limits on the allowed error for each code.
DS005671-18
FIGURE 9. Basic A/D Tester
4.0 MICROPROCESSOR INTERFACING
To dicuss the interface with 8080A and 6800 microproces-
sors, a common sample subroutine structure is used. The
microprocessor starts the A/D, reads and stores the results
of 16 successive conversions, then returns to the user’s
program. The 16 data bytes are stored in 16 successive
memory locations. All Data and Addresses will be given in
hexadecimal form. Software and hardware details are pro-
vided separately for each type of microprocessor.
4.1 Interfacing 8080 Microprocessor Derivatives (8048,
8085)
This converter has been designed to directly interface with
derivatives of the 8080 microprocessor. The A/D can be
mapped into memory space (using standard memory ad-
dress decoding for CS and the MEMR and MEMW strobes)
or it can be controlled as an I/O device by using the I/O R
and I/O W strobes and decoding the address bits A0
A7
(or address bits A8
A15 as they will contain the same 8-bit
address information) to obtain the CS input. Using the I/O
space provides 256 additional addresses and may allow a
simpler 8-bit address decoder but the data can only be input
to the accumulator. To make use of the additional memory
reference instructions, the A/D should be mapped into
memory space. An example of an A/D in I/O space is shown
in Figure 12 .
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