GE Understanding MM300 Dust Collector Communication Protocols

RS485 INTERFACE (MODBUS RTU) COMMUNICATIONS GUIDE

AL: low order byte of A

AH: high order byte of A

CRC: 16 bit CRC-16 value

i, j: loop counters

(+): logical exclusive or operator

Di: i-th data byte (i = 0 to N-1)

G:16 bit characteristic polynomial = 1010000000000001 with MSbit dropped and bit order reversed

shr(x): shift right (the LSbit of the low order byte of x shifts into a carry flag, a '0' is shifted into the MSbit of the high order byte of x, all other bits shift right one location

The algorithm is:

1.FFFF hex —> A

2.0 —> i

3.0 —> j

4.Di (+) AL —> AL

5.j+1 —> j

6.shr(A)

7.is there a carry? No: go to 8. Yes: G (+) A —> A

8.is j = 8? No: go to 5. Yes: go to 9.

9.i+1 —> i

10.is i = N? No: go to 3. Yes: go to 11.

11.A —> CRC

Timing

Data packet synchronization is maintained by timing constraints. The receiving device must measure the time between the reception of characters. If 3.5 character times elapse without a new character or completion of the packet, then the communication link must be reset (i.e. all slaves start listening for a new transmission from the master). Thus at 9600 baud a delay of greater than 3.5 x 1 / 9600 x 10 x = x 3.65 x ms will cause the communication link to be reset.

MM300 supported functions

The following functions are supported by the MM300:

•FUNCTION CODE 03 - Read Setpoints and Actual Values

•FUNCTION CODE 04 - Read Setpoints and Actual Values

•FUNCTION CODE 05 - Execute Operation

•FUNCTION CODE 06 - Store Single Setpoint

•FUNCTION CODE 07 - Read Device Status

•FUNCTION CODE 08 - Loopback Test

•FUNCTION CODE 10 - Store Multiple Setpoints

Modbus Functions

Function Code 03H

Modbus implementation: Read Holding Registers

4 MM300 MOTOR MANAGEMENT SYSTEM – COMMUNICATIONS GUIDE