Data Translation DT9820 Series, User Manual

Page: 38 / 112

Chapter 2
26
Digital I/O Features
This section describes the following features of the digital I/O
subsystem:
• Digital I/O lines, described on this page;
• Resolution, described on this page; and
• Operation modes, described on page 27 .
Digital I/O Lines
DT9820 Series function modules support eight digital input lines
(Port A, lines 0 to 7) through the DIN subsystem and eight digital
output lines (Port B, lines 0 to 7) through the DOUT subsystem. The
inputs are pulled up to +5 V through a 22 k
Ω
resistor.
You can use high-to-low transitions on digital inputs 0 to 3 to start
A/D conversions; you can use high-to-low transitions on digital
inputs 4 to 7 to stop A/D conversions. Refer to
page 14 for more
information.
Note: All the digital inputs must be in the high state before the
DT9820 Series module can detect a high-to-low transition on the
digital input lines. Therefore, if you are using the digital inputs to
trigger the A/D subsystems, it is recommended that you do not
perform a single-value operation on the DIN subsystem.
On power up or module reset, no digital data is output from the
modules. All the outputs include diode protection to the isolated
ground and the is5 V. In addition, you can externally power
the +5 V output so that the digital outputs retain their current values
when the module is powered down.