GE MOTOR MANAGER 2 User Manual

GE Power Management
MM2 Motor Manager 2 6-3
6 COMMUNICATIONS 6.1 MM2 MODBUS PROTOCOL
6
If a MM2 Modbus slave device receives a transmission in which an error is indicated by the CRC-16
calculation, the slave device will not respond to the transmission. A CRC-16 error indicates than one
or more bytes of the transmission were received incorrectly and thus the entire transmission should
be ignored in order to avoid the MM2 performing any incorrect operation.
The CRC-16 calculation is an industry standard method used for error detection. An algorithm is
included here to assist programmers in situations where no standard CRC-16 calculation routines
are available.
6.1.6 CRC-16 ALGORITHM
Once the following algorithm is complete, the working register "A" will contain the CRC value to be
transmitted. Note that this algorithm requires the characteristic polynomial to be reverse bit ordered.
The MSBit of the characteristic polynomial is dropped since it does not affect the value of the remain-
der. The following symbols are used in the algorithm:
—>: data transfer
A: 16 bit working register
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

GE MOTOR MANAGER 2 Specifications

General

Brand	GE
Model	MOTOR MANAGER 2
Category	Controller
Language	English