AD12-8
12-Bit 8-Input A/D Converter and Counter/Timer Card
FEATURES
- Eight
single-ended analog inputs
- 12-bit
resolution
- Up
to 40,000 conversions/second
- Programmable
scan rate
- Can
be used with AIM-16 to support up to 128 differential
inputs with programmable gains
- On-board
counter/timer for event counting, pulse and waveform
generation, and frequency measurement.
- Sixteen
bits of digital I/O
- Buffered
precision reference voltage output
FUNCTIONAL
DESCRIPTION
Model
AD12-8 is an 8-channel, 12-bit Analog-to-Digital converter
(A/D) and counter/timer card for ISA-bus computers. The
card is 7.0" long (178mm)and requires a full-size
expansion slot. All connections are made through a standard
37-pin male connector. Address setup is via DIP switches
on the card.
INPUT
SYSTEM EXPANSION
The
AD12-8 contains two control registers for controlling
up to eight 16-input multiplexer expanders model AIM-16.
This provides capability for up to 128 differential inputs
and different gains for each channel of those multiplexers.
Thus, you can mix widely different full-scale inputs on
a channel-by-channel basis.
For
for applications where negligible time skew between channel
samples is desired, AD12-8 can be used in conjunction
with Simultaneous Sample and Hold Card models SSH-xx.
Further, if aliasing of the analog input signals is a
consideration, then AD12-8-S03 can be used with
Anti-Alias Filter Card model AAF-xx.
ANALOG
INPUTS
Inputs
to the A/D are single-ended with common ground and can
withstand ±30 VDC overload and transients of several
hundred volts. The A/D is a successive- approximation
type converter with solid-state input analog multiplexer
and sample and hold amplifier. Full scale inputs of ±10
Volts, 0-10 Volts, and ±5 Volts are jumper selectable
and provide resolution of 4.88mV and 2.44mV respectively.
A/D conversion time is typically 25 microseconds.
COUNTER
TIMERS
An
8254 counter/timer chip that contains three 16-bit counters
is included. By means of a jumper, you can set up the
card to automatically start upon completion of a counter
cycle. Data from the previous conversion is stored in
dedicated registers to be read by the computer while the
conversion cycle is in progress. Counters #1 and #2 are
concatenated to 32 bits for this purpose and the clock
input is derived from a 1/32 multiple of the computer's
14.31818 MHz color oscillator. In this way, programs are
independent of the computer's CPU or I/O bus clock frequencies
and programs can be transported to other computers without
possibility of timing problems that could be caused by
those frequencies.
INTERRUPTS
AD12-8
can initiate interrupts at IRQ levels 2 through 7. These
interrupts can be initiated either by the A/D converter's
EOC signal at the end of each conversion or from an external
source via Pin 24 of the I/O connector. Selection of the
interrupt source is by jumper placement and interrupts
are enabled/disabled in software. Interrupt requests are
reset by writing to either of two control registers or
by occurrence of a computer Reset signal. That latter
removes any interrupt request that may occur at system
power up.
DISCRETE
DIGITAL I/O
The
AD12-8 also provides sixteen bits of individually jumper-programmable
digital I/O. (Note: If external AIM-16 expansion multiplexers
are to be used with the AD12-8, seven of these lines are
used for channel selection and gain control. Otherwise,
they may be used as digital outputs.) When set as an output,
power drivers provide 24 mA sink and 2.6 mA source capability.
OUTPUT
REFERENCE VOLTAGE
Model
AD12-8 also provides a precision 10 VDC (±0.1 VDC)
reference voltage output which is derived from the A/D
converter reference and may be used to provide sensor
excitation when required. This reference voltage output
is buffered and will source up to 220 mA. (Sufficient,
for example, for exciting a number of strain gages.)
