USB to SERIAL Adapter Voltage Levels w/ xtend module

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1

Will it damage the adapter if i try to communicate with a serial device that outputs over 5 volts? I connected the adapter to an xtend serial modem. The xtend documentation says
"The XTend OEM RF Modules interface to a host device through a TTL-level asynchronous serial
port. Through its serial port, the module can communicate with any UART voltage compatible
device or through a level translator to any serial device (For example: RS-232/485/422 or USB
interface board)."

I was powering the xtend module from a 5.39V battery. I am not sure but does that mean the xtend’s serial high will be 5.39 V? Will that damage my USB to serial adapter? It seems to have damaged it in some way, although it (the bad adapter) can still communicate with an identical (good) usb adapter with a crossover cable. The extend module is fine, I can communitcate with it via a carrier board using the good adapter. the carrier board Tx pin outputs a 6V peak to peak signal. The bad adapter can’t communticate (Rx) with this carrier board, though it did for a moment, then stopped. I am confused what is going on.

David

2

Hello,

5.39V doesn’t sound too high, but I wouldn’t recommend it; 6V is almost surely too high (so you definitely should not connect directly to the carrier board that gives you 6V out). The logic-level serial line is normally high, so you should be able to just look at the voltage with a meter when the line is idle; the serial adapter can handle up to 5V (and 5% tolerance, or 5.25V, should be safe).

- Jan