Data Translation DT9857, User Manual, Page: 103 / 192

Principles of Operation
103
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
DT9857 and DT9857E modules support one digital input port, consisting of 8 digital input
lines (lines 0 to 7) and one digital output port, consisting of 8 digital output lines (lines 0 to 7).
The resolution is fixed at 8 bits.
You can specify the digital I/O line that you want to read or write in a single-value digital I/O
operation. Refer to
page 103 for more information about single-value operations.
In addition, you can perform a continuous digital input operation by specifying the digital
input port in the analog input channel list, or a continuous digital output operation by
specifying the digital output port in the analog output channel list.
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
DT9857 and DT9857E modules support the following digital I/O operation modes:
• Single-value operations are the simplest to use but offer the least flexibility and efficiency.
You use software to specify the digital I/O port and a gain of 1 (the gain is ignored). Data
is then read from or written to all the digital I/O lines. For a single-value operation, you
cannot specify a clock or trigger source.
Single-value operations stop automatically when finished; you cannot stop a single-value
operation.
• Continuous digital input takes full advantage of the capabilities of the DT9857 and
DT9857E modules. Enter the digital input port (all 8 digital input lines) as channel 12 for
the DT9857-8 or DT9857E-8 module, or channel 20 for the DT9857-16 or DT9857E-16
module in the analog input channel list. You can specify a clock source, scan mode, trigger
source, buffer, and buffer wrap mode for the digital input operation. The input sample
clock (internal or external) paces the acquisition of data from the digital input port as well
as the analog input channels, tachometer input, general-purpose counter/timer, and the
measure counters if they are specified in the analog input channel list; refer to
page 79 for
more information.
• Continuous digital output takes full advantage of the capabilities of the DT9857 or
DT9857E module. Enter the digital output port (all 8 digital output lines) as channel 2 in
the analog output channel list. You can specify a clock source, trigger source, buffer, and
buffer wrap mode for the digital output operation. The analog output sample clock paces
the analog output and digital output operation. Refer to
page 85 for more information.