132 Rockwell Automation Publication 1756-UM058G-EN-P - November 2012
Chapter 7 Configure ControlLogix Digital I/O Modules
The tables below describe the communication and connection formats available 
for input modules.
Table 26 - Input Module Communication Formats
Communication Format Data Return Module
Input Data Module returns only general fault and input data. 1756-IA16, 1756-IA16I, 1756-IA32, 
1756-IB16I, 1756-IB16, 1756-IB32, 
1756-IC16, 1756-IG16, 1756-IH16I, 1756-IM16I, 
1756-IN16, 1756-IV16, 1756-IV32
CST Timestamped Input Data Module returns input data with the value of the system clock from its 
local chassis when the input data changes.
Rack Optimization The 1756-CNB module collects all digital input words in the remote 
chassis and sends them to the controller as a single rack image. This 
connection type limits the status and diagnostic information 
available.
Listen Only—Input Data These formats have the same definition as the similarly-named 
options above except that they are Listen-only connections.
Listen Only—CST Timestamped Input Data
Listen Only—Rack Optimization
Full Diagnostic Input Data Module returns input data, the value of the system clock from its 
local chassis when the input data changes, and diagnostic data.
1756-IA8D, 1756-IB16D
Listen Only—Full Diagnostic Input Data This format has the same definition as Full diagnostic input data 
except that it is a Listen-only connection.
1756-IA8D, 1756-IB16D
Table 27 - Input Module Connection Formats
Connection Format Input Data Data Return Module
Data Timestamp Data Module returns input data with COS timestamps in CIP Sync system 
time. To configure per point timestamping, see page 87
.
1756-IB16IF
Data Module returns input data without COS timestamps. This format is 
useful when the highest possible throughput is required.
Data with Event Timestamp Data Results in two input connections:
• Connection to return input data with COS timestamps in CIP Sync 
system time.
• Connection to initiate event tasks. See page 93
.
Listen Only Timestamp Data These formats have the same definition as those above except that 
they are Listen-only connections.
Data
Listen Only with Event Timestamp Data