Friday, July 8, 2011

PLC Operating Modes

A PLC of Modicon Micro can be constructed to run in one of three methods:
Single mode—running as a programmable control system of standalone, supervision its own resources of fixed I/O.
Parent mode— running as the one PLC on a link running I/O expansion whose CPU can handle the resources of fixed I/O of all the PLCs on that connection.
Child mode—running as a PLC on a link of I/O expansion, permitting some or all of its resources of fixed I/O to be managed and contacted by the parent PLC on the connection.

The Link of I/O Expansion
The link of I/O expansion contains a parent PLC and 1 to 4 child PLCs linked through standard six-position cables of telephone. Every cable has a connector of RJ11 on both ends. Connections of PLC-to-PLC are made at the port of RS-485 (exp link) on each unit. Only a PLC on the link can be constructed as the parent. The other PLCs on the connection have to be constructed as child PLCs. A PLC in mode of single operating cannot be used on the link of expansion. Every child PLC is addressed uniquely with a child ID # in the range #1- #4. The resources of fixed I/O the child PLCs can be controlled and contacted by logic running in the parent.

Expansion of A120 I/O
The PLCs of 110CPU512 and 110CPU612 are prepared with a 30-pin expansion port that permits the units to correspond with A120 I/O racks. This port is committed to communications of A120 I/O.

The PLCs of 110CPU311 and 110CPU411 do not support expansion of A120 I/O. With expansion of A120 I/O, 2 ... 4 racks are interrelated along a physically mounted of parallel bus on DIN rail. The PLC itself is constantly constructed as rack 1, and the housing of A120 I/O are constructed as racks 2 ... 4. The expansion of A120 I/O can be used by the PLC in any of its three modes of operating. A120 I/O can be contacted only by the PLC to which it is linked. This way that the program of ladder logic driving the A120 I/O and all the connected mapping of A120 I/O have to be saved in the PLC to which the A120 I/O is associated.

If a child PLC on a link of serial I/O expansion employs expansion of A120 I/O, the A120 I/O connected with that child cannot be contacted by the parent on the link.

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