GE GFK-0787B user manual Input Processing, Discrepancies, Discrete Inputs

4

Input Processing

During the Input Scan portion of the CPU sweep, the PLC receives inputs from the discrete and analog input blocks. It stores the input data in different areas of memory as described below.

After the Input Scan, the GMR logic performs voting on the inputs configured for GMR redundancy, and places the results into the discrete and analog input tables where they are available to the application program.

Discrepancies

If there is a discrepancy between the original input data for an input and the voted input state, the GMR software automatically places a message in the I/O Fault Table, where it is available to the Logicmaster 90 software and the application program logic. Also, fault bits that report the discrepancy fault for each voted input are available to the application program, so it can take appropriate action if a discrepancy fault occurs. Discrepancy faults are latched. Discrepancy reporting is discussed in the chapter on Diagnostics.

Discrete Inputs

During the Input Scan, data from discrete input blocks is placed in the Input Table as shown below. Inputs from blocks that have been included in the GMR configuration is placed in the areas labelled A, B, and C. Data from any additional discrete input blocks (non-voted GMR blocks or blocks on other busses) is placed in a separate area as shown.

Discrete Input Table

Input
Voting
Logic
Bus A inputs	A
Bus B inputs	B
Bus C inputs	C

Voted Inputs

Non-voted Inputs

Reserved inputs

The GMR software creates and maintains the separate areas of the discrete Input Table. In addition to the four areas used for the inputs received from Genius blocks, there are two additional areas. The first, at the beginning of the Input Table, is for voted inputs.

The other, at the end of the table, is for ªreservedº inputs, which are used to inhibit diagnostics for outputs that are being controlled manually.

The chapter on Programming explains in detail how the Discrete Input table memory is allocated.

GFK-0787B Chapter 4 PLC Subsystem 4-7