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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.

PLC A

C

P

U

PLC B

C

P

U

PLC C

C

P

U

Multidrop Cable

RS±232/422

Converter

Multidrop cable is catalog number IC690CBL714 (1 cable). Two cables are needed for 3 CPUs.

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.

GFK-0787B

Chapter 1 Introduction

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GE GFK-0787B user manual Series 90-70 PLCs, Inter-processor Communications