22 Rockwell Automation Publication 1756-UM058G-EN-P - November 2012
Chapter 2 Digital I/O Operation in the ControlLogix System
The table defines some of the delay factors that affect the signal propagation on
an I/O module.
Output Modules
ControlLogix output modules receive a signal from the controller and process it
internally via hardware and an ASIC scan before sending a signal to the output
device via the RTB.
Delay Description
Hardware How the module is configured and the variance between the type of modules affects
how the signal is processed.
Filter User configuration varies between modules, thus affecting the signal propagation.
ASIC ASIC scan = 200 µs.
A typical delay time can be estimated despite the number of factors that might
contribute. For example, if you are turning on a 1756-IB16 module at 24V DC in
25 °C (77 °F) conditions, the signal propagation delay is affected by these
factors:
• Hardware delay to energize the input (typically 290 µs on the
1756-IB16 module)
• User-configurable filter time of 0, 1, or 2 ms
• ASIC scan of 200 µs
In the worst case scenario with a filter time of 0 ms, the 1756-IB16 module has
a 490 µs signal propagation delay.
These times are not guaranteed. For nominal and maximum delay times for
each module, see the 1756 ControlLogix I/O Modules Specifications Technical
Data, publication 1756-TD002
.
Hardware DelayASIC Delay
42702
Signal Sent from
RTB Output Point
Signal Received
from Controller
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