Measurement Computing PCM-DAC02 - Manual (Page 9)

The maximum current supplied by the analog outputs is 2.5 mA. Loads drawing
higher currents than this will cause the analog output to droop, meaning that a code of
4095 will not be able to generate a full scale voltage of 5V, but one somewhat less.
It is best to group the ground on pin 1 with the analog output on pin 2, and the ground
on pin 3 with the analog output on pin 4
3.5 EXTERNAL INTERRUPT INPUT
The PCM-DAC02 pin 5 is the input to a circuit which will generate an interrupt to the
computer. The interrupt must be enabled through software. The interrupt is level
sensitive and is triggered on a TTL high level. TTL high is approximately 2.5V to
5V. The interrupt signal you provide should transition from a low of 0, or ground, to
a high of 5V.
The procedure initiated by an interrupt is wholly dependent on programming.
3.6 DIGITAL INPUTS & OUTPUTS
The PCM-DAC02 has eight bi-directional digital I/O lines. The eight digital lines
may be programmed as input or output in groups of: eight inputs, eight outputs or four
inputs and four outputs.
A register controls the direction of the digital I/O lines and must be set via software.
At power on or reset the digital lines default to inputs.
Please note: Digital lines in an input state present a high impedance to any device
connected to them. The implication is that if you are using a digital line to control the
input of a TTL chip, and that digital line turns from an output to an input, the TTL
chip being controlled MAY detect the turned around line as a “1” or a “0”. This could
cause the TTL input being controlled to switch on or off, possibly with consequences
for the system you are controlling. To prevent random switching and force all digital
lines into a known state on power up or reset, use pull up or pull down resistors to fix
the state of the line as either high or low. A properly selected resistor will not interfere
with TTL level output signals.
For more information on programming the digital I/O lines, please refer to the
Universal library programmers manual.
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