AccuEnergy AcuRev 2000, User Manual

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contents. The result is shifted towards the least signifcant bit (LSB), with a zero filled into
the most signifcant bit (MSB) position. The LSB is extracted and examined, if the LSB
equals to 1, the register is exclusive ORed with a preset, fixed value; if the LSB equals to 0, no
action will be taken. 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’s current
value, and the process repeats for eight more shifts as described above. The final 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 first, followed by the
high-order byte.
Addr Fun
Data start
reg hi
Data start
reg lo
Data #of
regs hi
Data #of
regs lo
CRC16
Hi
CRC16
Lo
06H 03H 00H 00H 00H 21H 84H 65H
Figure 5-3 Protocol Illustration
Addr: Slave device address
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 registers, high byte
Data #of reg lo: Number of registers, low byte
CRC16 Hi: CRC high byte
CRC16 Lo: CRC low byte
5.2 Modbus Communication Format