Ascii Transmission Mode; Supported Modbus Function Codes; (0X01) Read Coils - Hitachi HX-RIO3 Series User Manual

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A.2.2. ASCII Transmission Mode
When devices are setup to communicate on a MODBUS serial line using ASCII (American Standard Code
for Information Interchange) mode, each 8–bit byte in a message is sent as two ASCII characters. This
mode is used when the physical communication link or the capabilities of the device does not allow the
conformance with RTU mode requirement regarding timers management.
Start Address
1 char 2 chars
A.3. Supported MODBUS Function Codes
Function
Code
1 (0x01)
2 (0x02)
3 (0x03)
4 (0x04)
5 (0x05)
6 (0x06)
8 (0x08)
15 (0x0F)
16 (0x10)
23 (0x17)
Refer to MODBUS APPLICATION PROTOCOL SPECIFICATION V1.1a
-
A.3.1. 1 (0x01) Read Coils
This function code is used to read from 1 to 2000 contiguous status of coils in a remote device. The
Request PDU specifies the starting address, i.e. the address of the first coil specified, and the number of
coils. In the PDU Coils are addressed starting at zero. Therefore coils numbered 1-16 are addressed as
0-15. The coils in the response message are packed as one coil per bit of the data field. Status is indicated
as 1= ON and 0= OFF.
•
Request
Field name
Start of Frame
Slave Address
Function Code
Starting Address Hi
Starting Address Lo
Quantity of Outputs Hi
Quantity of Outputs Lo
Error Check (CRC/LRC)
End of Frame
Function
2 chars
Function
Read Coils
Read Discrete Inputs
Read Holding Registers
Read Input Registers
Write Single Coil
Write Single Register
Diagnostics (Serial Line
only)
Write Multiple Coils
Write Multiple registers
Read / Write Multiple
register
Example
-
0x07
0x01
0x10
0x00
0x00
0x0A
-
-
Data
Up to 252 chars
Description
Read output bit
Read input bit
Read output word
Read input word
Write one bit output
Write one word output
Read diagnostic register
Write a number of output bits
Write a number of output words
Read a number of input words /
Write a number of output words
RTU
t1-t2-t3
0x07
0x01
0x10
0x00
0x00
0x0A
0xB8, 0xAB
t1-t2-t3
HX-RIO3 Series
CRC Check End
2
2 chars
CR,LF
Unicast
Broadcast
Unicast
Unicast
Unicast
Unicast
Unicast / Broadcast
Unicast / Broadcast
Unicast
Unicast / Broadcast
Unicast / Broadcast
Unicast
chars
/