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Pointing to ModBus Bits


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When using the Turbo PMAC I would setup an M-Var to point to a ModBus TCP bit like below, How do I do the same thing with the Power PMAC?


;Setup for General Purpose Bits (a value of 0 or 1)

; Modbus adresses 400001:00 to 400016:15 (256 total available regiters)

; M-Vars 3301 to 3556

M3301->X:$10780,0,1 ; Modbus 400001:00

M3302->X:$10780,1,1 ; Modbus 400001:01

M3303->X:$10780,2,1 ; Modbus 400001:02

M3304->X:$10780,3,1 ; Modbus 400001:03

M3305->X:$10780,4,1 ; Modbus 400001:04

M3306->X:$10780,5,1 ; Modbus 400001:05

M3307->X:$10780,6,1 ; Modbus 400001:06

M3308->X:$10780,7,1 ; Modbus 400001:07

M3309->X:$10780,8,1 ; Modbus 400001:08

M3310->X:$10780,9,1 ; Modbus 400001:09


M3311->X:$10780,10,1 ; Modbus 400001:10

M3312->X:$10780,11,1 ; Modbus 400001:11

M3313->X:$10780,12,1 ; Modbus 400001:12

M3314->X:$10780,13,1 ; Modbus 400001:13

M3315->X:$10780,14,1 ; Modbus 400001:14

M3316->X:$10780,15,1 ; Modbus 400001:15

M3317->Y:$10780,0,1 ; Modbus 400002:00

M3318->Y:$10780,1,1 ; Modbus 400002:01

M3319->Y:$10780,2,1 ; Modbus 400002:02

M3320->Y:$10780,3,1 ; Modbus 400002:03

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On a Server, there is Sys.ModbusServerBuffer[].


As far as I have been able to tell, there is no counterpart when Power PMAC is a Client. But, there are the ModbusRegisterRead and ModbusRegisterWrite commands which specify Modbus registers and corresponding PMAC variables.


See attached documents.

Power PMAC Modbus Command Specification 2014-01.pdf

power pmac modbus design document.pdf

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If you intend to access individual bits, ModbusCoilRead/ModbusCoilWrite may be better options--coils are individual bits, whereas registers are full bytes.


As a master, the next best option would be to use a PLC that would copy from some other registers (Sys.Udata[] or equivalent) into the appropriate Modbus registers. This would add some delay, as the data would only get sent to the modbus registers at the PLC's run rate, but it would allow you to map pointers to individual bits.

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