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 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.
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.
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.
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.)