Communication Format - IDEC SmartAXIS FT9Z-1A01 User Manual

11: M C
ODBUS OM M UN I CATI ON

Communication Format

This section describes the communication format for each function code from the slave number up to immediately before the
check code.
Function Code 01 (Read Coil Status) and Function Code 02 (Read Input Status)
Function code 01 reads bit device statuses of Q (output), R (shift register), or M (internal relay). One through 128 consecutive bits
can be read out.
Function code 02 reads bit device statuses of I (input), T (timer contact), or C (counter contact). One through 128 consecutive bits
can be read out.
Communication Frame
Request from Modbus Master
Slave No.
xxh
ACK Reply from Modbus Slave
Slave No.
xxh
NAK Reply from Modbus Slave
Slave No.
xxh
Communication Example
Read 15 bits starting at output Q10.
Q10  (1 – 0)  8 + 0 + 1 = 9
Purpose Modbus address: 9
9 – 1 = 8 = 8h
Communication frame address: 0008h
Slave No. 8
Condition
Q10 through Q27 binary data: 1234h
RTU Mode

Request from Modbus Master
ACK Reply from Modbus Slave
NAK Reply from Modbus Slave
11-12
Function Code Address
01h / 02h xxxxh
Function Code Quantity of Data
01h / 02h xxh
Function Code Error Code
81h / 82h xxh
08 01 0008 0010 (CRC)
08 01 02 34 12 (CRC)
08 81 xx (CRC)
S A XI S P
M AR T
No. of Bits
xxxxh
First 8 Bits
xxh
/ L U ' M FT9Y-B 1378
R O I TE SER S ANUAL
Second 8 Bits
xxh
Last 8 Bits
xxh