Rockwell Automation T7491 ICS Regent+Plus Mixed I/O Modules - Manual (Page 10)

Multiplexed I/O Module (T7491)
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Industrial Control Services
different module type. Figure 5 illustrates how the slot keys
are installed on the I/O chassis slot field wiring connectors.
The slot key positions for the multiplexed I/O module are
listed in Table 1.
Figure 5. Installing Slot Keys.