Measurement Computing CIO-DAS800 - Manual (Page 11)

4.8 SINGLE-ENDED ANALOG INPUTS
The board accepts single-ended inputs only. Each input has two wires connected to the CIO-DAS800; a
channel high (CH# HI) and a Low Level Ground (LLGND). The LLGND signal must be the same
ground the PC is on. The CH# HI is the voltage signal source in the range of +/-5V maximum.
4.9 DIGITAL OUTPUTS & INPUTS
The digital inputs and outputs on the CIO-DAS800 are TTL level. TTL is an electronics industry term,
short for Transistor Transistor Logic, which describes a standard for digital signals. For a listing of the
TTL level specifications for these digital lines, please see the specifications at the end of this manual.
There are three digital inputs and four digital outputs. The digital outputs are controlled by a register on
the board and are updated each time the register is written to. The digital inputs are buffered by a
register on the board. Each time the register is read, the current high/low state of the digital I/O lines is
obtained. The lines are pulled high so a one (1) is read when no signal is connected to an input
Typically, the digital lines are used to control external expansion boards (all four outputs) and to trigger
and gate A/D conversions (IP0 input).
4.10 COUNTER TIMER CIRCUIT
There is an 82C54 counter/timer on the board which can be used to:
O Pace analog conversions
O Measure frequency
O Count events
O Precisely time intervals
The Universal Library has software to support the timer. The connections to the hardware are explained
here. For detailed information on the 82C54 registers, please refer to the Intel or AMD data sheet for this
part if you wish to program the 82C54 registers directly.
The 82C54 contains three counters, each is 16 bits wide. Of the three counters, two are dedicated to
pacing analo-to-digital conversions. These two, CTR1 and CTR2, when not in use by the A/D, are
available for other tasks but are limited to some extent by access to I/O pins. The first counter, CTR0, is
available for user applications.
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