Modbus (jun 1, 1970 – dec 1, 1974)
Description:
In the early 1970’s communications between PLCs started to develop. Modbus was introduced as the first industrial communications network. This communication network was based on a Master/Slave architecture using messaging to communicate between Modbus nodes. Its original interface ran on RS-232 but later implementations used RS-485 to allow for quicker communications that could run longer distances. However, the lack of standardization and changing technology made PLC communications a nightmare.
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PLC History
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