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1-3GFK-0787B Chapter 1 Introduction
Series 90-70 PLCs
A GMR system normally consists of one to three identical CPUs running identical
application software. Each CPU is connected to the same input and output subsystems.
Each CPU receives all inputs and performs voting for discrete inputs and mid-value
selection for analog inputs. Each CPU computes the required outputs as a function of the
inputs and the application program logic.
Inter-processor Communications
The PLCs exchange initialization data at startup, then operate asynchronously. They
communicate regularly using Global Data. Each Genius bus scan, each PLC broadcasts up to
64 words of Global Data. This includes 8 words of system information. An additional 56
words of Global Data are available for use by the application program. Redundancy is also
built into Global Data communications. Each message is sent twice, using different busses.
The PLCs may also be joined in a multidrop Series Ninety Protocol (SNP) network. A host
computer on the network can be used for gathering data from the system. In addition, the
SNP network permits convenient program updates using the Logicmaster 90 programming
software and the Program Download utility included on the GMR software diskette.
C
P
U
C
P
U
C
P
U
RS–232/422
Converter
Multidrop Cable
PLC A
Multidrop cable is catalog number
IC690CBL714 (1 cable). Two cables
are needed for 3 CPUs.
PLC CPLC B
All other normal Series 90-70 communications interfaces are also available. If required
for the application, the host software should collect data from each CPU and perform
the necessary voting.