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Machine language
Control program reduced to binary form.
MAP (manufacturing automation protocol)
"Standard" developed to make industrial devices communicate more easily. Based on a seven-layer model of communications.
Master
The master on a network is the device that controls communication traffic. The master of a network usually polls every slave to check if it has something to transmit. In a master-slave configuration, only the active master can place a message on the bus. The slave can reply only if it receives a frame from the master that contains a logical token that explicitly enables the slave to reply.
Master control relay (MCR)
Hardwired relay that can be deenergized by any hardwired series-connected switch. Used to deenergize all devices. If one emergency switch is hit it must cause the master control relay to drop power to all devices. There is also a master control relay available in most PLCs. The master control relay in the PLC is not sufficient to meet safety requirements.
Memory map
Drawing showing the areas, sizes, and uses of memory in a particular PLC.
Mnemonic codes
Symbols designated to represent a specific set of instructions for use in a control program. An abbreviation given to an instruction: usually an acronym that is made by combining the initial letters or parts of words.
ModBus
Protocol originally developed by Modicon, now part of Schneider Automation.
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