Rockwell Automation T8311 Trusted Expander Interface - Manual (Page 14)

Trusted
TM
Module T8311
Issue 12 Mar 07 PD-T8311 14
3. Application
3.1. Message Forwarding
The primary function of the Expander is to provide a method of extending the IMB beyond a single
processor chassis. The active TMR Expander Interface Module receives messages from the
processor chassis IMB/backplane and forwards them to the Expander Bus when its slot position is
enabled. Similarly, the active TMR Expander Processor Module forwards all messages received from
the Expander Bus to the addressed Expander Chassis IMB.
For other command messages the response message received by the active Expander Processor
from the addressed module is passed to the Expander Bus and hence to the TMR Expander Interface
Module. The active TMR Expander Interface Module then passes the message to the Processor
Chassis IMB, subject to the prevailing IMB control signals.
The messages received from the controller chassis IMB at the TMR Expander Interface Module are
re-synchronised and majority voted (Byzantine voted) before being passed to the triplicated Expander
Bus. Similarly, messages received by the TMR Expander Processor Module from the Expander
Chassis IMB are re-synchronised and majority voted before onward transmission.
Messages received from the Expander Bus at both the TMR Expander Interface Module and TMR
Expander Processor Module are re-synchronised and majority voted before being passed to the
associated IMB.
Errors in messages are corrected, and therefore masked using this method. This, however, makes it
important that discrepancies in faults in these signals are detected and the information made available
for fault reporting purposes to avoid latent fault issues.
3.2. Control Signal Forwarding
The active TMR Expander Processor Module continually monitors and transmits the state of the
following signals:
All three signals are fully triplicated. These signals are distributed to all of the attached Expander
Busses. The TMR Expander Processor Modules forward the received state of these signals to the
Expander Chassis IMB. The direction of these signals is always from TMR Processor to TMR
Expander Interface to TMR Expander Processor to interface (I/O) module.
As with the message forwarding, these signals are re-synchronised and majority voted, i.e. Byzantine
voted at the TMR Expander Interface and TMR Expander Processor Modules. The signals are
synchronous within the Expander Chassis even in the case of a fault within the Processor Chassis.
• Power Failure Warning
• System Watchdog
• Command Response Control