Data Translation DT7837, Руководство пользователя, Страница: 47 / 98

Principles of Operation
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Digital I/O Features
This section describes the following features of digital I/O operations:
• Digital I/O lines
• Operation modes
Digital I/O Lines
DT7837 modules support one digital input port, consisting of up to 8 digital input lines (lines
0 to 7) and one digital output port, consisting of up to 8 digital output lines (lines 0 to 7). The
resolution is fixed at 8 bits.
By default, general-purpose input pins 1 to 8 of the Digital connector on the DT7837 module
correspond to digital input signals 0 to 7. Similarly, general-purpose output pins 11 to 18 of the
Digital connector on the DT7837 module correspond to digital output signals 0 to 7.
Note: If you assigned a general-purpose input signal as a counter clock or gate input or as
an external trigger, you can read the value of the signal as you would any other digital input
signal, if desired.
If you want to write a value to a specific digital output line, ensure that the corresponding pin
of the Digital connector is not configured for another use (such as the output of the
counter/timer) or you could corrupt the signal on the pin.
A digital line is high if its value is 1; a digital line is low if its value is 0. On power up or reset,
a low value (0) is output from each of the digital output lines and a high value (1) is read from
each of the digital input lines if the lines are not connected.
Operation Modes
DT7837 modules support the following digital I/O operation modes:
• Synchronous read and write operations – Using software, you can read the value of the
digital input port using a synchronous read operation or write a value to the digital
output port using a synchronous write operation. The operation is blocking, in that it does
not return until the value is read or written.
You do not specify a trigger or clock for a synchronous read or write operation. The
operation stops automatically once the value is read or written.
• Continuous digital input – Using software, enter the digital input port (all 8 digital input
lines) as specify bit 7 of the channel mask in the input stream. You can specify the
sampling frequency and trigger source for the input stream. The trigger starts the
acquisition. The input sample clock paces the acquisition of data from the digital input
port as well as the analog input channels, tachometer input, general-purpose
counter/timer, and/or the measure counter.