20
Communication Guide
The standard connection conforms to the Modbus specifications, sepecially 2 wire
multidrop serial bus diagram, presented at the website of Modbus.org in 2002
(Modbus_over_serial_line_V1.pdf, Nov.2002). Simple wiring diagram is like below.
The characteristics is like below in case of a direct connection to the bus.
Items Contents
Type of trunk cable single, shielded, twisted pair cable.
Min 3rd cable
Maximum length of the bus 1000m (3,2181 ft) (at 19.2kbps)
Maximum number of 32 stations (31 slaves)
stations without repeater
�20m (66ft, at 1 tapoff)
Maximum length of tapoffs �40m (131ft, divided by tapoff no.
in Multi-Junction Box)
�450 - 650ΩPullup resistor, 5V basis
�450 - 650ΩPulldown resistor,
Bus polarization Recommend the polarization to Master at
Common. There is no polarization at
RS485 of EOCR .
Line terminator 120ΩResistor, + /- 5%
Common polarity YES (connect 1 protection ground minimum
to the bus)
Standard connection