5-2
IM 77C01H01-10EN
5.1 Overview
For MODBUS communication with the UPM100, 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 (ASCII)
8 bits (binary)
Message start mark
: (colon)
Not necessary
Message end mark
CR+LF (*2)
Not necessary
Message length (*1)
2N+1
N
Data time intervals
1 second or less
24 bit time or less (*3)
Error detection
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 UPM100 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.
*3: Theoretically, points of termination are detected at an interval of 24-bit time in the RTU mode.
In the case of the UPM100 however, this detection is carried out at a time interval in multiples
of 0.833 milliseconds. If the Baud rate is 9600 bps, the time interval is 1 ÷ 9600 x 24 seconds or
shorter.
In MODBUS communication, a higher-level device identifies each UPM100 with a station
number of 1 to 99.
Note
• The UPM100 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.
Содержание UPM100
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