PLC Allen Bradley Addressing

Use this table as quick reference for addressing

Addressing mode	Guidelines
2-slot	· Two I/O module slots=1group · Each physical 2-slot I/O group correspond to one word (16 bits) in the input image table · When you use 16-point I/O modules, you must install as a pair an input and output module in an I/O group; if you use an input module in slot 0, you must install to an output module in slot 1 (or it must be empty) · You can not use a block transfer module and 16-point module in the same I/O group, because block transfer modules use 8 bits in both input and output image table. Therefore, 8 bits of the 16 point module would conflict with the block transfer module. · You can not use 32-point I/O module · Assign one I/O rack number to eight I/O groups
1-slot	· One I/O module slot = 1 group · Each physical in the chassis correspond to one word (16 bits) in the input image table and output image table · When you use 32-point I/O modules, you must install as a pair an input module and output module in 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) · Use any mix of 8- and 16-point I/O modules, block transfer or intelligent modules in a single I/O chassis · Assign one I/O rack number to eight I/O groups
½-slot	· One half of an I/O module slot = 1 group · Each physical slot in the chassis correspond to two words (32bits) in the input image table and two words in the output image table. · Use any mix of 8-, 16-, and 32-point I/O or block transfer and intelligent modules. · With the processor-resident local rack set for ½-slot addressing, you can not 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, ½-slot addressing), you can not force the input bits for word 1 (I:001) on or off. · Assign one I/O rack number to eight I/O groups.