
B-63003EN-2/01 Chapter 3 Installing the Startup Ladder 3 - 5
3
PMC Instructions
There are two types of PMC instructions which can be used to program your ladder logic.
Basic Instructions
There are 14 basic PMC instructions which the processor can be programmed to execute. They
include reading from and writing to addresses, boolean functions (AND, OR, NOT), and stack
register operations (shift left, shift right). The CPU has a 9-bit operation stack register which it uses
to store intermediate results of logical operations while running the sequence program.
In the example from Figure 3-2, there are five relay contact symbols and five corresponding PMC
instructions. The CPU would execute the sequence program as follows:
1
.
Read in the signal of address X0.0.
2.
Read in the status of address R10.1 and perform logical AND
with X0.0.
3.
Read in X6.1 and logically OR it with the previous result.
4.
Read in R20.3, invert the signal, and perform logical AND
with previous result.
5.
Write the result out to address Y0.0
Functional Instructions
It would be very hard to write a sequence program using just the basic instructions mentioned above.
Some functions, such as the function for controlling the rotation via the shorter path, would be
extremely time-consuming to program.
Therefore, GE Fanuc provides a comprehensive library of functional instructions in addition to the 14
one-bit logical operations. Functional instructions including timers, counters, and decoders are made
available to programmers, allowing them to develop ladder code which takes advantage of each
machine tool’s specific application needs. A complete list of instructions is given in the GE Fanuc
PMC Model PA1/PA3/RA1/RA2/RA3/RB/RB2/RB3/RB4/RB5/RB6/RC/RC3/RC4/NB/NB2 Ladder
Language Programming Manual (publication no. B-61863E).