Yokogawa JUXTA VJ Series Limit Alarms Instrukcja Użytkownika Pobierz pdf (Strona 41)

5-1

IM 77J01J11-01E 3rd Edition : Oct. 15, 2007-00

5. MODBUS Communication

5.1 Overview

The use of MODBUS communication allows the VJ Series signal conditioners to

communicate with a PC. In this communication, a PC reads data from D registers,

internal registers of the VJ Series.

Hereafter, PCs are generally called "higher-level devices."

Maximum overall cable length of 1200 m

for a maximum of 31 substations

050101E.EPS

Figure 5-1 Example of Connection for MODBUS Communication

See Also

Chapter 6 for information on the D registers.

For MODBUS communication with the VJ Series, 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) Not necessary

Message end mark

Message start mark

CR+LF Not necessary

Message length (*1)

Error detection

2N+1 N

Data time intervals 1 second or less 24 bit time or less (*2)

Longitudinal redundancy check: LRC Cyclic redundancy check: CRC-16

050102E.EPS

*1: When message length in the RTU mode is assumed to be "N"

*2: For a communication rate of 9600 bps, 1⫼9600⫻24 seconds or less applies.

In MODBUS communication, a higher-level device identifies each VJ Series signal condi-

tioner with a communication address of 1 to 99.

1 2 ... 36 37 38 39 40 41 42 43 44 45 46 ... 59 60

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