YOKOGAWA PR300, User Manual

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5-2
<Toc> <Ind> <5. Modbus/RTU and ASCII Communication Protocols>
IM 77C01E01-10E
For Modbus communication with the PR300, we provide the ASCII mode and RTU mode
(binary system) for the transmission mode.
Table 5.1 ASCII and RTU Modes
Item ASCII Mode RTU Mode
Number of data bits 7 bits (ASCII) 8 bits (binary)
: (colon) None
Message end mark
Message start mark
CR+LF
(
*
2)
None
Message length
(
*
1)
Error detection
2N+1 N
Data time intervals 1 second or less Between frames: 3.5 characters
Longitudinal redundancy check: LRC Cyclic redundancy check: CRC-16
*1: When message length in the RTU mode is assumed to be “N”, message length in ASCII mode is “2N+1”.
*2: LF is a synchronization character indicating that the PR300 is ready to accept the next signal. In the RTU mode,
synchronization is achieved during the time interval between characters. If there is a period of time equivalent to 3.5
characters before the next character is received, the message being received next is recognized as a new frame.
In Modbus communication, a higher-level device identifies each PR300 with a station
number of 01 to 99.
NOTE
• The PR300 has data (D register) the unit of which is two words. When 2-word data
need to be written or read, writing or reading operations must be performed for the 2-
word data at the same time.
• Even if data written to the D register is out of the effective range, a normal response is
returned.