Rockwell Automation 1785-LTx,D17856.2.1 Classic PLC-5 Programmable Controllers Users Manual - Manual (Page 45)

Assigning Addressing Modes,
Racks, and Groups
Chapter 4
4-3
An I/O rack is an addressing unit that corresponds to 8 input image-table
words and 8 output image-table words. A rack contains 8 I/O groups.
13074
0 1 2 3 4 5 6 7
I/O Group Numbers .
Depending on I/O chassis size and I/O group size, an I/O rack can occupy
a fraction of an I/O chassis, a full I/O chassis, or multiple I/O chassis.
Select an addressing mode for each chassis independently, based on the
type and density of the I/O modules contained therein. When you select
addressing mode, limit the number of remote I/O adapters and I/O modules
to the maximum number that the PLC-5 processor can support.
Using 2ĆSlot Addressing
When you select 2-slot addressing, the processor addresses two I/O
module slots as one I/O group. Each physical 2-slot I/O group corresponds
to one word (16 bits) in the input image table and one word (16 bits) in the
output image table. The type (unidirectional or bidirectional) and density
of a module that you install determines the number of bits that are used in
each word.
Important: You cannot use 32-point I/O modules with 2-slot addressing.
Choosing the
Addressing Mode