Rockwell Automation MAI32AD 32-Analogue Input Module Differential Input - Manual (Page 12)

12 MAI32*AD 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.
Figure 2-6 Common interface -Block diagram
The microcontroller co-ordinates I/O signal processing, signal path diagnostics, on-line/off-line
status and signal status read/write cycles to and from the MPPs 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 extinguishes the Health LED on the I/O
module front panel in the event of a microcontroller failure, LFD action or a voting discrepancy.