Appendix
RS485 standard
The RS485 standard
•Polarization
•Line termination
•Distribution of a reference potential
•Number of slaves
•Length of bus
It does not specify the connector type or pinout.
The Modbus specification published on www.modbus.org in 2002 contains precise details of these characteristics. They are also summarized in the next sections (Modbus
Modbus 2-wire standard schematic
The standard schematic corresponds to the Modbus specification published in 2002 on www.modbus.org (Modbus_over_serial_line_V1.pdf, Nov 2002) and, in particular, to the
Schematic diagram
Master
R | G | 5 V |
|
650 Ω
650 Ω
0 V
| D1 |
120 Ω | 120 Ω |
1n F | 1n F |
| D0 |
| Common |
R
G
Slave 1
R
G
Slave n
62 | S1A53844 01/2011 |