1-4 Series 90™-70 Enhanced Hot Standby CPU Redundancy User's Guide May 2000 GFK-1527A
1
Redundancy CPUs as Compared to Other Series 90-70 CPUs
The Redundancy CPU has several differences in operation compared to other Series 90-70 CPUs.

Features not Available with Redundancy CPUs

The following features are not available:
I/O Interrupts: This includes the single edge triggered interrupts from the discrete input
modules, the high alarm and low alarm interrupts from the analog input modules, and
interrupts from third party VME modules. A program that declares I/O Interrupt triggers
cannot be stored t o a Redundancy CPU.
Timed Interrupts
VME Integrator Racks.
Stop I/O Scan mode: If an attempt is made to place the PLC in this mode, the PLC will reject
the selection and return an err or .
Flash operation: User Flash (Store/Load, Verify) as opposed to Flash firmware upgrade
FBCs and FIP I/O
Timed and Event-triggered Programs: Logic that contains Timed or Event-triggered programs
cannot be stored .
Microcycle Mode and Periodic Programs
14-point interrupt module
OVR_PRE %S reference which indicates whether one or more overrides is active

Differences in Operation for Redundancy CPU s

The following features operate differently with the CGR772 or CGR935 than they do with other
Series 90-70 CPUs:
RUN/DISABLED mode. This is explained in chapter 4, Operation.
Configuration of Fault Actions
STOP to RUN mode transition
Background Window Time (default is different)
C Debugger
Ethernet Global Data operation is enhanced
Rack 7 is not available