SHENZHEN ENCOM ELECTRIC TECHNOLOGIES CO. enc eds800-2s0002n User Manual page 122

10.4 RTU Communication Mode：
10.4.1 Data frame format
Using RTU mode, messages are sent at least 3.5 character time interval pause. The
first transmitted field is device address, the character you can transfer is hexadecimal
0x00 ~ 0xFF. Network equipment Continuously monitor the bus, including pauses.
When the address field is received, all equipment determine whether it is sent to
their own. when the last character of the packet transfer is complete, at least a 3.5
character times pause mean the end of the message. A new message can begin after
this pause.
The entire message frame must be transmitted as a continuous flow. If a new
message start transmitting in less than 3.5 character times after a message and then
receiving device will consider it a continuation of the previous message. This will
cause an error, because in the final CRC field value can not be right.
RTU frame format as the talbe below：
Frame Header
Slave address
Communication command code
Data content DATA
Data content DATA
......
......
CRC check value low byte
CRC check value high byte
Closing Flag
Regarding generation method of CRC check value, please refer to part 10.8
for check method.
10.4.2 Host read slave parameter
Command code 03H. Host can read or one or more parameter( up to ten) by
initiating a communication transaction .
E.g., read 2 contiguous inverter parameter values from the address 0000H of
inverter whoes address is 01, the contents of host command：
Parameters initial address high byte
Parameters initial address low byte
Number of parameter high byte
Number of parameter low byte
CRC check value low byte
CRC check value high byte
The contents of slave reply：
EDS800 series Service Manual
ADR
CMD
ADR
CMD
3.5 characters time pause
Slave value：1~127
03H：read slave parameter
06H：write slave parameter
The contents of packet:
Parameter address（16bit）;
Number of parameter or bytes of parameter
value;
Parameter value（16bit）
16bit Unsigned check value
3.5 characters time pause
Be calculated
Be calculated
117
01H
03H
00H
00H
00H
02H
01H
03H