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8-1. Message transmission mode
There are two types of modes namely RTU (Remote Terminal Unit) mode and ASCII mode and
they are selected using the front key setting.
<Table 1 Comparison between RTU mode and ASCII mode>
Item RTU mode ASCII mode
Interface
RS-232C､RS-422A､RS-485
Communication system Half duplex asynchronous system
Communication speed 2400,4800,9600,19200,38400bps
Transmission code Binary ASCII
Vertical direction Parity Error check
(Error
detection)
Horizontal
direction
CRC-16 LRC
Start bit 1 bit
Data length 7 bit/8 bits
Parity bit None/even/odd
Character
configuration
Stop bit 1 bit/2 bits
Message start code None : (Colon)
Message end code None CR, LF
Data time interval Less than 28 bit time Less than 1 second
8-1-1. Transmission data
RTU mode is binary forwarding. ASCII mode splits the RTU 8 bit binary into high order and low
order 4 bits and garbles each character (0 to 9, A to F).
Example) RTU mode
ASCII mode
67H
36H ("6")
89H
37H ("7")
ABH
38H ("8")
39H ("9")
41H ("A")
42H ("B")
As the length of message in RTU mode is half that of ASCII mode and hence effective transmission
is done.
8-1-2. Configuration of the message frame
RTU mode is made up of message part only.
ASCII mode is made up of start character ": (Colon, 3AH)", message and end character "CR
(Carriage return, ODH) + LF (Line feed, 0AH)".
RTU mode ASCII mode
Message : Message CR LF
ASCII mode has a strong point that, as the start character is ":" it facilitates troubleshooting.
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