Maximum serial interface cable length?

1

Hi

Just wondering if anybody has already experimented with how long the 4-way (GND, +5, TXD, RXD) serial wires can be extended (without having to use line conditioning etc) running at 115200 baud reliably?

Or, if you haven’t experimented with limits, are you running any extension, and how long?

2

From http://wiki.tjc1688.com/doku.php?id=10.常见问题集锦:1.基础问题集锦

2. How many meters can the serial communication line connect?

TTL communication: If the communication value is 2 meters under the 9600 TTL transmission, the actual application is recommended not to exceed 50cm. This has a relationship with the electromagnetic environment, which is mainly limited by the load capacity and anti-interference ability of the TTL device.

232 communication: RS-232-C standard stipulates that the drive is allowed to have a capacitive load of 2500pF, and the communication distance will be limited by this capacitor. For example, when using a communication cable of 150pF/m, the maximum communication distance is 15m; if the power per meter is As the capacity is reduced, the communication distance can be increased. Another reason for the short transmission distance is that RS-232 is a single-ended signal transmission, which has common ground noise and cannot suppress common mode interference. Therefore, it is generally used for [rs232 (9-pin) interface] communication within 15m.

4

I think that’s the best answer you are going to get. “It depends”, and it depends on the things listed in the wiki. Not all cables and input/output stages are created equal, so your answer is going to be unique to your situation based on the factors listed above.

5

I am planning to do a product with a 2m cable extension.
Did you experiment with the cable length?
If yes, what were your conclusions?
We will order custom made cables so we have the possibility of selecting cable preferences as we wish.
I feel pretty confident that it can be done but you never know until you’ve tried/someone have tried…

6

Depends on the baud rate. 9600 will most probably work. For higher speeds, I’d add RS232 driver ICs on both sides to get true bipolar signals and to have enough drive strength for the capacitive load which such a long cable is. MCU outputs are normally specified for capacitive loads up to 25 or 50pF, but 1m of cable represents something between 100 and 200pF.