3onedata GW11 Series User Manual page 70

When using ASCII mode, each 8-bit byte in the message is converted to 2 ASCII
characters for transmission. The main advantage of the ASCII mode is that the
characters can allow up to 1 second intervals without error.
RTU and ASCII mode comparison
Type
Coding
System
Bits per Byte
Error check
Modbus TCP
The Modbus protocol defines a simple protocol data unit (PDU) independent of the
underlying communication layers. The mapping of Modbus protocol on specific buses
or network can introduce some additional fields on the application data unit (ADU).
General Modbus frame:
The Modbus application data unit is built by the client that initiates a Modbus
transaction. The function indicates to the server what kind of action to perform.
RTU and ASCII mode comparison
RTU
8-bit binary
Two hexadecimal
contains 8-bits of data within
each ASCII character of the
message
1 start bit
8 data bits
Odd / even parity 1 bit
No odd / even parity check
If there is a odd / even parity check for 1 stop bits
If there is no odd / even parity check for 2 stop bits
CRC
3onedata proprietary and confidential
Copyright © Shenzhen 3onedata Technology Co., Ltd.
(I)GW11XX Modbus User Manual
ASCII
Hexadecimal
character One hexadecimal
contains 4-bits of data within
each ASCII character of the
message
1 start bit
7/8 data bits
LRC
character
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