Allen-Bradley MicroLogix 1200 Reference Manual page 65

Addressing Modes
The MicroLogix 1200 and MicroLogix 1500 support three types of data
addressing:
• Immediate
• Direct
• Indirect
The MicroLogix 1200 and 1500 do not support indexed addressing.
Indexed addressing can be duplicated with indirect addressing. See
Example - Using Indirect Addressing to Duplicate Indexed Addressing on
page 4-7.
How or when each type is used depends on the instruction being
programmed and the type of elements specified within the operands of
the instruction. By supporting these three addressing methods, the
MicroLogix 1200 and 1500 allow incredible flexibility in how data can be
monitored or manipulated. Each of the addressing modes are described
below.
Immediate Addressing
Immediate addressing is primarily used to assign numeric constants within
instructions. For example: You require a 10 second timer, so you program
a timer with a 1 second time base and a preset value of 10. The numbers
1 and 10 in this example are both forms of immediate addressing.
Direct Addressing
When you use direct addressing, you define a specific data location
within the controller. Any data location that is supported by the elements
of an operand within the instruction being programmed can be used. In
this example we are illustrating a limit instruction, where:
• Low Limit = Numeric value (from -32,768 to 32,767) entered
from the programming software.
• Test Value = TPI:0.POT0 (This is the current position/value of
trim pot 0.)
• High Limit = N7:17 (This is the data resident in Integer file 7,
element 17.)
The Test Value (TPI:0.POT0) and High Limit (N7:17) are direct addressing
examples. The Low Limit is immediate addressing.
Programming Instructions Overview
Publication 1762-RM001C-EN-P
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