SmartAlarm Instruction Manual Rev 2
Page 102 of 115
MODBUS RTU
The tables below show the standard message formats for data interchange for
Modbus RTU protocol.
RTU tables.
Each character represents 8 bit binary data in
hexadecimal format.
Y represents a character with more than one possible
value.
All characters are framed with 1 start bit, 1 parity bit and 1
stop bit.
Read Request
– Master
RTU
START
ADDRESS
FUNCTION
REGISTER /
COIL
ADDRESS
NO. OF
REGISTERS /
COILS
ERROR
CHECK
STOP
ELAPSED TIME 3
½
CHARACTERS
MIN
Y
Y
YY
YY
YY
ELAPSED TIME
3 ½
CHARACTERS
MIN
Read Response - Slave
RTU
START
ADDRESS
FUNCTION
BYTE
COUNT
DATA
ERROR
CHECK
STOP
ELAPSED
TIME 3 ½
CHARACTERS
MIN
Y
Y
Y
YY
YY
ELAPSED
TIME 3 ½
CHARACTERS
MIN
Single Write Request/Response
Master write request and slave write response, are the same.
RTU
START
ADDRESS
FUNCTION
REGISTER /
COIL
ADDRESS
DATA
ERROR
CHECK
STOP
ELAPSED
TIME 3 ½
CHARACTERS
MIN
Y
Y
YY
YY
YY
ELAPSED
TIME 3 ½
CHARACTERS
MIN