The first step in industrial computer serial port transformation is often stuck in card selection: should I buy a 232 card or a 485/422 card? The interface shapes of the three are similar, but the electrical characteristics are completely different. If you choose the wrong one, the communication will not be stable, and the port will be burned. The following three steps will be used to explain the selection logic clearly.

Let's look at the level first: single-ended and differential are the watershed

RS232 uses a single-ended signal, using the wire-to-ground voltage to represent 0 and 1, and has weak resistance to common-mode interference; RS422 and RS485 use differential signals, which are determined by the voltage difference between the two wires, so the noise generated by on-site motors and frequency converters is difficult to affect it. RS422 is point-to-point full-duplex, and RS485 can connect multiple nodes on the same pair of lines. It is the mainstream choice for production line buses at present.

Let's look at distance and speed: don't exceed the experience value

• The common transmission distance of RS232 is generally no more than 15 meters, and the rate is typically 9600bps to 115200bps;
• The bus length of RS485/422 can be about 1200 meters at 9600bps, and the rate can be increased to more than 1Mbps at short distances;
• The distance is roughly inversely proportional to the speed. When wiring, it is recommended to leave a margin according to the conservative value of half speed and half distance.

Decide which card to buy according to the networking method

One-to-one debugging of old equipment, choose the standardPCI-E serial port cardThat's it; if you want multiple buses or one bus to connect multiple instruments, you should choose a differential card, for examplePCI-E to 4-port RS485/422 serial port card, each port can be independently configured in 485 or 422 mode. Please refer to the planning ideas for the overall factory network.Industrial automation and machine vision network solutions.

When you are not sure whether the field is 232 or 485, first connect the number lines on the terminal row: only the TX, RX, and GND lines are mostly 232. Those marked A, B or 485+, 485- are differential buses, and then allocate cards accordingly. If you have any questions, please consult EB-LINK engineers at 0755-83179002.