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FAQs
Q1: What is the primary function of the 1756-RM2?
The 1756-RM2 is an Enhanced Redundancy Module that supports fully redundant controller architectures. It automatically cross-loads programs from the primary to the secondary controller, maintains synchronization through continuous data exchange, and ensures automatic switchover if the primary controller fails.
Q2: How many 1756-RM2 modules are required for a redundant system?
Two modules are required per system — one in the primary chassis and one in the secondary chassis. The modules communicate via fiber optic cables (1756-RMC1, RMC3, or RMC10).
Q3: Can the 1756-RM2 be used with the legacy 1756-RM module?
No. The 1756-RM2 does not communicate with the 1756-RM. When upgrading an existing system, both the primary and secondary chassis must use 1756-RM2 modules. The 1756-RM2 is also not compatible with 1756-RM/A, 1756-RM/B, or 1756-RMXT modules.
Q4: What controllers are compatible with the 1756-RM2?
The 1756-RM2 is compatible with 1756-L6x and 1756-L7x series controllers (including L71, L72, L73, L74, L75). Enhanced redundancy systems require firmware version 19.053 or higher for L7x controllers, or 16.057/16.081/19.052 or higher for L6x controllers.
Q5: What are common causes of "Redundancy Disqualified" errors with the 1756-RM2?
Common causes include:
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Firmware version mismatch between primary and secondary controllers or communication modules
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Network issues — the EN2T/EN2TR modules in both chassis must be on the same subnet and able to communicate (event log message: "Partner not on same link")
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Loose module connections — check processor and communication module seating in the backplane
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Incorrect firmware — ensure redundant firmware is properly flashed to the 1756-RM2 modules
