Saturday, July 9, 2011

Addressing I/O on an Expansion Link of Micro PLC

A link of I/O expansion is made by daisy sequencing up to 5 Micro PLCs together through cable links at their ports of RS-485. One PLC has to be constructed as the parent, and the rest units have to be constructed as child PLCs.

The Parent PLC
The parent PLC can address all its resources of own fixed I/O as well as any resources of fixed I/O residing in the child PLCs. The locations of fixed I/O of the parent PLC are addressed automatically for you.

A Child PLC
The operating system of ladder logic supposes by default that all the points of fixed I/O existing on that PLC will be controlled by the parent PLC on the network when you choose child PLC operating mode for a PLC. Therefore, no values are assigned to the I/O map of a child PLC in its default state. The fixed I/O locations in the child can be mapped in a screen associated with the parent’s I/O map.
Note Any I/O of A120 linked to a child PLC has to be addressed by the child PLC. The I/O of A120 in a child PLC can’t be controlled or accessed by the parent PLC via the link of I/O expansion.

Fixed I/O Controlled by the Parent PLC
The system being constructed in the example contains of two PLCs of 110CPU51200, a child and one parent, on an expansion link of I/O. The three screens of I/O map from MODSOFT Lite. When you construct the parent, ensure that it is set for at least a child. The system operating will not permit the parent PLC to access any of the resources of child’s I/O except you have specific the reality of that child in the parent’s configuration PLC. Screens 1 and 2 demonstrate the maps of I/O for the fixed locations of I/O in the child and parent PLC that will be controlled by orientations in the parent’s memory of PLC. Both screens of I/O map are contacted while the panel of programming is linked to the parent.

Observe that the types of location used in the map of I/O for the child place all the existing fixed relay output and discrete input locations of the child PLC under the control of the parent PLC. The maps of MIC128 all 16 of the child’s 24 VDC inputs to locations 10017 ... 10032 in the memory of parent PLC and the 12 outputs of relay to locations 00017 ... 00032 in the data memory of parent’s user.

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