Computer Interfacing
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MAX3535 extremely high error rate

Lots of errors with MAX3535


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Author Message

Jan 19, 2009 11:48 pm

I am using, or trying to use, a link with MAX3535 isolated transceivers. The problem is that the error rate is very high. It's so high that it's hard to measure, but could be 1% or more. At 700 bytes/second, it's too high.

The test setup is one master and one slave board, both on my test bench, both running from the same power supply. They are connected via Cat-5 cable.

I have tried:
- Half duplex
- Full duplex
- Different values of termination resistors
- No termination resistors
- Connecting the grounds on the isolated side
- Not connecting the grounds
- Replacing my hardware with two of the Maxim MAX3535EEVKIT evaluation boards. No difference.
- Contacting Maxim tech support. Their only real advice was to try the eval board.
- Adding software to the slave board to use a spare serial port to dump error status messages to the PC. It reveals that I am getting overrun, parity, and framing errors. I am not using parity, but the fault bit is sometimes set anyway.

The only thing that made any difference was that I removed the MAX3535 completely, and hardwired the master Tx directly to the slave Rx, and vice versa. I ran this test for about 6 hours ( > 2 million bytes) with zero errors. So, I am guessing that software is not the problem.

I was going to try a "normal" (non-isolated) transceiver, but Maxim doesn't make an eval board for any of them, and I didn't want to take the time to make my own. Of course, for the time I've spent on it, I could have made a board by gnawing the copper off with my teeth.

Anyway, my question, at long last, is this: Does anybody have any experience with this device? Am I doing something wrong, or is a high error rate the price to pay for isolation?

Gary Olmstead
Toucan Technology
Ventura CA

Oct 28, 2009 7:18 pm

Hello, I use the MAX3535 in a slot machine of my design with no trouble at all. I am not using the isolation, grounds are commoned, CAT-6 cables and 120ohm termination with 1K pull up/pull downs. I am linking my games in promiscuous mode. The most successful approach I've found is to designate a single master which steers the flow of communication to all linked slaves.

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