【Introduction】
When faced with a wiring scenario of 100 meters in a workshop, should you choose RS232, RS422, or RS485? The core differences among the three are immediately apparent: RS232 supports only 15 meters of point-to-point communication, RS422 can reach 1200 meters but is limited to unidirectional transmission, while RS485, with its 1200-meter transmission distance and the ability to connect 32 nodes, has become the absolute mainstream in industrial sites. However, choosing the right type is just the beginning. Failing to configure a 120Ω termination resistor can lead to signal reflection, using ordinary twisted pair cables instead of shielded cables can cause interference, and exceeding the ground potential difference can burn out chips—these minor mistakes can paralyze the system. The following will detail three practical techniques: selecting shielded cables, configuring dynamic resistance, and multi-level grounding, teaching you how to avoid 90% of communication failures from the source.
1. Connect M to the cable shield
2. A=TxD/RxD -(green wire/pin 8)
3. B=TxD/RxD +(red wire/pin 3)
Note:
Pin 3 – RS485 signal B(+)
Pin 8 – RS485 signal A(-)
Pin 5 – Connect to the shielded equipotential point
RS422 Wiring:
· Pins 2 and 9 – RS422 transmit signal
Pins 3 and 8 – RS422 receive signal
· SHELL connects to the shielded equipotential point
RS485 Wiring:
Pin 3 – RS485 signal B(+)
· Pin 8 – RS485 signal A(-)
· Pin 1 – equipotential point
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