3.1 Basic Functionality
Registers
3-19
3
CPU Unit Functionality
Registers
Registers are areas that store data within the Machine Controller. Variables are registers with labels (vari-
able names).
There are two kinds of registers: global registers that are shared between all programs, and local registered
that are used only by a specific program.
Global Registers
Global registers are shared by ladder programs, user functions, motion programs, and sequence programs.
Memory space for global registers is reserved by the system for each register type.
Local Registers
Local registers can be used within each specific drawing. These registers cannot be shared by other draw-
ings. Local registers are stored in the program memory for each drawing.
Ladder Program Conceptual Diagram
Ladder
program
User functions
Motion
programs/
sequence
programs
Global registers
S registers
65,535
words
M registers
1,048,576
words
G registers
2,097,152
words
I registers
65,536
words
Input data +
Monitor
para
CPU interface
inputs
O registers
65,536
words
Output data +
Setting
para
CPU interface
outputs
C registers
16,384
words
H01
FUNC01
FUNC02
H
Parent drawing
# registers
Child drawing
# registers
User function
X registers
User function
X registers
D registers
D registers
Y registers
Z registers
# registers
D registers
Y registers
Z registers
# registers
D registers
These registers cannot be shared between
different drawings.
These registers cannot be shared between
different drawings.