Reference Guide

PMAC Quick Reference Guide

62 PLC Programs

• PLC2: Since PLC1 is suggested as an initialization PLC (and can run potentially only once on

power-up), PLC2 is the first PLC in the remaining sequence from 2 to 31. This makes PLC2 the ideal

place to copy digital input information from I\O expansion boards like the Acc-34 into its image

variables. This way, PLCs 3 to 30 could use the input information, writing the necessary output

changes to the outputs image variables.

• PLC3 to PLC30: PLC programs are useful particularly for monitoring analog and digital inputs,

setting outputs, sending messages, monitoring motion parameters, issuing commands as if from a

host, changing gains, and starting and stopping moves. By their complete access to PMAC variables

and I/O and their asynchronous nature, they become very powerful adjuncts to the motion control

programs.

• PLCC3 to PLCC30: Compiled PLCs are convenient for its faster execution compared to regular

PLCs. Since the execution rate of compiled PLCs is the same as some of the safety checks (following

error limits, hardware overtravel limits, software overtravel limits, and amplifier faults), PLCCs are

ideal to replace or complement them. However, due to its limited allocated memory space, PLCCs

should be reserved only for faster execution critical tasks.

• PLC31: This is the last executed PLC in the sequence from 1 to 31. PLC31 is recommended for

copying the output image variable (changed in lower number PLCs executed previously) into the

actual outputs of an I\O expansion board like, for example, the Acc-34A.

Entering a PLC Program

PLCs are programmed in the same way as motion programs are in a text editor window for later

downloading to PMAC.

Before starting to write the PLC, make sure that memory has not been tied up in data gathering or

program trace buffers, by issuing DELETE GATHER and DELETE TRACE commands.

1. Open the buffer for entry with the OPEN PLC n statement, where n is the buffer number. Next, if

there is anything currently in the buffer that should not be kept, it should be emptied with the CLEAR

statement (PLC buffers may not be edited on the PMAC itself; they must be cleared and re-entered).

If the buffer is not cleared, new statements will be added onto the end of the buffer.

2. When finished, close the buffer with the CLOSE command. Opening a PLC program buffer

automatically disables that program. After it is closed, it remains disabled, but it can be re-enabled

again with the ENABLE PLC n command, where n is the buffer number (0--31). I5 must also be set

properly for a PLC program to operate.

3. At closing, PMAC checks to make sure all IF branches and WHILE loops have been terminated

properly. If not, it reports an error, and the buffer is inoperable. Then correct the PLC program in

the host and re-enter it (clearing the erroneous block in the process, of course). This process is

repeated for all of the PLC buffers to be used.

Because all PLC programs in PMAC’s memory are enabled at power-on/reset, it is good practice to have

I5 saved as 0 in PMAC’s memory when developing PLC programs. This will allow PMAC to be reset

and have no PLCs running (an enabled PLC only runs if I5 is set properly) and recover more easily from a

PLC programming error.

Structure Example:

DELETE GATHER

DELETE TRACE

OPEN PLC n CLEAR

{PLC statements}

ENABLE PLC n