GE 90-30 PLC Series Installation And Hardware Manual page 417

SNP Multidrop
Appendix
I
SNP Multidrop Overview
As used in this appendix, the term "SNP Multidrop" refers to a system that allows a programmer
(called the "master or host"), such as a personal computer running GE programming
software, to connect to two or more PLCs or intelligent Option modules (called "slaves") via a
single connection. In this arrangement the programmer is able to program, configure, test,
troubleshoot, etc., any one of the multidropped devices from one connection point.
Physically, a typical SNP multidrop system consists of a programmer and two or more PLCs
interconnected by a "daisy-chain" type cabling arrangement, as shown in the figure below. It is
necessary to assign each slave device (PLC or Option module) a unique SNP (Series Ninety
Protocol) address, using programming software such as Logicmaster, VersaPro, or Logic
Developer-PLC. The SNP address is used by the programmer to designate which PLC it will
communicate with. The SNP protocol uses the RS-422 communications standard. Note that the
PLCs or Option modules do not communicate with each other over the multidrop system. They
only communicate with the programmer. And only one device, the one designated by the
programmer, can communicate with the programmer at a time.
Multidrop Connector
15-pin Male
Multidrop
Connector
15-pin Female
Figure I-1. Series 90-30 Multidrop Example
GFK-0356Q
Multidrop Connector
15-pin Male
Series 90-30 PLC (slave)
Multidrop Cable
IC690ACC901
Serial Cable
Multidrop Connector
15-pin Male
Series 90-30 PLC (slave)
Multidrop Cable
Programmer (master)
Series 90-30 PLC (slave)
I-1