GN-9371_2_3 User Manual
Page 82 of (110)
G-series GN-9371_2_3 PIO Rev. 1.02.docx
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.
1 char 2 chars 2 chars Up to 252 chars 2 chars
CR,LF
A.3 Supported MODBUS Function Codes
Function Description Unicast / Broadcast
8 (0x08)
only)
Read diagnostic register Unicast
Write a number of output bits
Write a number of output words
23 (0x17)
Read / Write Multiple
register
Read a number of input words /
Write a number of output words
Unicast
- Refer to MODBUS APPLICATION PROTOCOL SPECIFICATION V1.1a
A.3.1 (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
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