Rockwell Automation 1785 PLC-5 User Manual download pdf (Page 51)

Publication 1785-UM012D-EN-P - July 2005

Addressing I/O and Controller Memory 4-7

Addressing

Block-Transfer Modules

Block-transfer modules occupy 8 bits in the controller’s I/O image table.

Since all block-transfer modules are bidirectional, they cannot be used to

complement either input or output modules.

Addressing Summary

Use this table as a quick reference for addressing.

To Address Use

single slot modules assigned I/O rack and group number of the slot in which the

module resides and 0 for the module number

When using 1/2-slot addressing, use the assigned rack

number and the lowest group number and 0 for the module

number.

double-slot modules assigned rack number and the lowest group number and 0 for

the module number

Addressing

Mode Guidelines

2-slot • Two I/O module slots = 1 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

• When you use 16-point 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 use of I/O.

• You cannot use a block-transfer module and a 16-point module in the same I/O group because

block-transfer modules use 8 bits in both the input and output table. Therefore, 8 bits of the

16-point module would conflict with the block-transfer module.

• You cannot use 32-point I/O modules.

• Assign one I/O rack number to eight I/O groups.

1-slot • 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 32-point 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

use of I/O.

• Use any mix of 8- and 16-point I/O modules, block-transfer or intelligent modules in a single I/O

chassis. Using 8-point modules results in fewer total I/O.

• Assign one I/O rack number to eight I/O groups.

1/2-slot • 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 8-, 16-, and 32-point I/O or block-transfer and intelligent modules. Using 8-point

and 16-point I/O modules results in fewer total I/O.

• With the controller-resident local rack set for 1/2-slot addressing, you cannot force the input

bits for the upper word of any slot that is empty or that has an 8-point or 16-point I/O module.

For example, if you have an 8-point or a 16-point I/O module in the first slot of your local rack

(words 0 and 1 of the I/O image table, 1/2-slot addressing), you cannot force the input bits for

word 1 (I:001) on or off.

• Assign one I/O rack number to eight I/O groups.

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Rockwell Automation 1785 PLC-5 User Manual Page 51

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