Rockwell Automation MDO16FNS 16-Channel Digital Output Module 120Vac/dc - Manual (Page 10)

10 MDO16FNS October 2005 – Issue 4
Triguard SC300E
Common Interface
The three discrete control circuits in the common interface (A, B, and C) are each responsible
for the control of the corresponding one third of the I/O module circuits. Each control circuit
comprises a microcontroller with a dedicated watchdog, data buffers and shared RAM. The
circuit is powered via the module and permits live insertion of replacement modules.
The microcontrollers co-ordinate I/O signal processing, signal path diagnostics, on-line/off-line
status and signal status read/write cycles to and from the SC300E processors via an I/O
communications bus. All I/O modules have an identification code which is read by the common
interface and passed to the MPPs for verification. The on-line/off-line status is determined by
the MPPs. If, for maintenance purposes, the On/Off Line Request switch on the front of the
module is operated, the action is read by all three microcontrollers and the request passed to
the MPPs which may then grant the request. The watchdog on each microcontroller
extinguishes the Health LED on the I/O module front panel in the event of a microcontroller
failure, LFD failure or a voting discrepancy.