2-18
Functional Description
Digital I/O Features
DAS-1800HC Series boards contain four digital inputs (DI0 to DI3) and
eight digital outputs (DO0 to DO7). Logic 1 on an I/O line indicates that
the input/output is high (greater than 2.0V); logic 0 on an I/O line
indicates that the input/output is low (less than 0.8V). The digital inputs
are compatible with TTL-level signals. These inputs are provided with
10k
Ω
pull-up resistors to +5V; therefore, the inputs appear high (logic 1)
with no signal connected.
Using Digital Inputs and Outputs
You can use the digital inputs and outputs for any general-purpose task,
except as follows:
●
If using an external digital trigger and gate, you must use digital input
line DI1/TGIN to attach the trigger/gate signal; in this case, you
cannot use DI1/TGIN for general-purpose digital input.
●
If using an external pacer clock, you must use digital input line
DI0/XPCLK to attach the external pacer clock signal; in this case,
you cannot use DI0/XPCLK for general-purpose digital input.
When the analog inputs are either disabled or timed by an external pacer
clock, the digital I/O can be “paced” with interrupts generated by the
onboard pacer clock.
Using Digital Control Signal DOSTB
The DAS-1800HC Series boards provide a strobe signal (DOSTB) for the
purpose of strobing data through the digital outputs and latching the data
into a register in other equipment. Where DAS-1800HC Series boards use
the positive edge of the strobe to strobe data out, you must use the
negative edge to strobe data into other equipment because the negative
edge gives you a 300ns lag to allow for delays. Data is valid until the next
strobe, as shown in Figure 2-6.
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