Measurement Computing CIO-DAS801 - Manual (Page 16)

CIO-DAS801 User's Guide Functional Details
16
Digital inputs and outputs
All the digital inputs and outputs on the CIO-DAS801 are TTL level. TTL is an electronics industry term, short
for Transistor Transistor Logic, with describes a standard for digital signals which are either at TTL low or
TTL high; levels which are detected by all other TTL devices.
The CIO-DAS801 has three digital inputs and four digital outputs. 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
digital outputs are controlled by a register on the board and are updated each time the register is written to. The
lines are pulled high so a logical-one is read if no signal is connected to an input.
The digital lines also are used to control external EXP boards (all four outputs) and to trigger and gate A/D
conversions (DIn 1).
Counter/timer circuit
The CIO-DAS801 has an 82C54 counter timer which can be used to perform the following tasks:
 Pace analog conversions
 Measure frequency
 Count events
 Time intervals
The software to support the timer is in the Universal Library. The connections to the hardware are explained
here. For detailed information on the 82C54 registers, refer to the 82C54 data sheet at
www.mccdaq.com/PDFmanuals/82C54.pdf .
The 82C54 contains three 16-bit counters (CTR0, CTR1, and CTR2). CTR1 and CTR2 are dedicated to the
pacing of analog to digital conversions. CTR1 and CTR2 are available for other tasks when not in use by the
A/D, but are limited to some extent by the wiring and access to I/O pins. CTR0 is available for your use.
Figure 8 shows the connections to the counters. It also shows the 82C54 functions, I/O pins and how these are
connected on the CIO-DAS801.