User manual

POWER INSTRUMENTS

the CRC. Start and stop bits, and the parity bit, do not apply to the CRC. During

generation of the CRC, each 8-bit character is exclusive ORed with the register

contents. Then the result is shifted in the direction of the least significant bit

(LSB), with a zero lled into the most signicant bit (MSB) position. The LSB is

extracted and examined. If the LSB was a 1, the register is then exclusive ORed

with a preset, xed value. If the LSB was a 0, no exclusive OR takes place. This

process is repeated until eight shifts have been performed. After the last (eighth)

shift, the next 8-bit byte is exclusive ORed with the register current value, and

the process repeats for eight more shifts as described above. The nal contents

of the register, after all the bytes of the message have been applied, is the

CRC value. When the CRC is appended to the message, the low-order byte is

appended rst, followed by the high-order byte.

Format of communication

Explanation of frame

Addr Fun Data start

reg hi

Data start

reg lo

Data #of

regs hi

Data #of

regs lo

CRC 16

06H 03H 00H 00H 00H 21H 84H 65H

Table 5.3 Explanation of frame

In table 5.3, the meaning of each abbreviated word is,

Addr: address of slave device

Fun: function code

Data start reg hi: start register address high byte

Data start reg lo: start register address low byte

Data #of reg hi: number of register high byte

Data #of reg lo: number of register low byte