Allen-Bradley SLC 500 Series

Publication 1747-RM001G-EN-P - November 2008
SLC Communication Instructions 12-35
Table 12.15 Modbus RTU Master Control Block
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
Word 0 EN ST DN ER CO EW NR TO Error Codes
Word 1 Not Used - Always 0 Target Node
Word 2 Number of Elements
Word 3 Target Data Address (decrement user input by 1)
Word 4 Reserved (unused, default to 0) Start-Bit/Coil/Input at
Physical Address
Word 5 Reserved (unused, default to 0) Register
Size
Word 6 Not Used - Always 0
Word 7 Not Used - Always 0 Reserved (Internal Messaging Bits) WQ
Word 8 Reserved (Internal Messaging Bits) Message Timer Preset
Word 9 Message Timer Scaled Zero
Word 10 Message Timer Accumulator
Word 11 Reserved (Internal Messaging Bits)
Word 12 AO=
0
Reserved (Internal Messaging Bits)
Word 13 Reserved (Internal Messaging Bits)