Rockwell Automation 1785-LTx,D17856.2.1 Classic PLC-5 Programmable Controllers Users Manual - Manual (Page 51)

Assigning Addressing Modes,
Racks, and Groups
Chapter 4
4-9
Summary
Table 4.A summarizes the guidelines for selecting an addressing mode.
Table 4.A
Addressing Mode Summary
Addressing
Mode
Guidelines
2Ćslot • Two I/O module slots = 1 group
• Each physical 2Ćslot I/O group corresponds to one word (16 bits) in the input image table and one word
(16 bits) in the output image table
• When you use 16Ćpoint I/O modules, you must install as a pair an input module and an output module in
an I/O group; if you use an input module in slot 0, you must use an output module in slot 1 (or it must be
empty). This configuration gives you the maximum usage of I/O.
• You cannot use a blockĆtransfer module and a 16Ćpoint module in the same I/O group because
blockĆtransfer modules use 8 bits in both the input and output table. Therefore, 8 bits of the 16Ćpoint
module would conflict with the blockĆtransfer module.
• You cannot use 32Ćpoint I/O modules.
1Ćslot • One I/O module slot = 1 group
• Each physical slot in the chassis corresponds to one word (16 bits) in the input image table and one
word (16 bits) in the output image table
• When you use 32Ćpoint I/O modules, you must install as a pair an input module and an output module in
an even/odd pair of adjacent I/O group; if you use an input module in slot 0, you must use an output
module in slot 1 (or it must be empty). This configuration gives you the maximum usage of I/O.
• Use any mix of 8Ć and 16Ćpoint I/O modules, blockĆtransfer or intelligent modules in a single I/O chassis.
Using 8Ćpoint modules results in fewer total I/O.
1/2Ćslot • One half of an I/O module slot = 1 group
• Each physical slot in the chassis corresponds to two words (32 bits) in the input image table and two
words (32 bits) in the output image table
• Use any mix of 8Ć, 16Ć, and 32Ćpoint I/O or blockĆtransfer and intelligent modules. Using 8Ćpoint and
16Ćpoint I/O modules results in fewer total I/O.
• With the processorĆresident local rack set for 1/2Ćslot addressing, you cannot force the input bits for the
upper word of any slot that is empty or that has an 8Ćpoint or 16Ćpoint I/O module. For example, if you
have an 8Ćpoint or a 16Ćpoint I/O module in the first slot of your local rack (words 0 and 1 of the I/O
image table, 1/2Ćslot addressing), you cannot force the input bits for word 1 (I:001) on or off.
The number of racks in a chassis depends on the chassis size and the
addressing mode:
If using this
chassis size:
With 2Ćslot
addressing,
rack type is:
With 1Ćslot
addressing,
rack type is:
With 1/2Ćslot
addressing,
rack type is:
4Ćslot 1/4 rack 1/2 rack 1 rack
8Ćslot 1/2 rack 1 rack 2 racks
12Ćslot 3/4 rack 1Ć1/2 racks 3 racks
16Ćslot 1 rack 2 racks 4 racks
Assigning Racks