USB Logic Analyzer - Negative Voltage Input?

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1

I haven’t found anything that tells me whether the [USB Logic Analyzer can tolerate negative voltage to the inputs. I’m intending to diagnose an RS-232 signal from a [MAX3232 transceiver, which potentially has a -5V to +5V range. The transceiver supply is 5VDC. Will this damage the analyzer?](SparkFun Transceiver Breakout - MAX3232 - BOB-11189 - SparkFun Electronics)](USB Logic Analyzer - 24MHz/8-Channel - TOL-18627 - SparkFun Electronics)

2

Most likely not; the inputs either go straight to the inputs on the processor or through a buffer chip. Either of those options are limited to a 0-5v range. Connect the analyzer to the LOGIC side of the transceiver instead as that end is 0-5v.

/mike

3

Thanks for the answer. I tested the TTL side and it looks like I got the RX and TX lines reversed. I’m seeing expected data on the TX line for some reason.

4

That’s a common mistake. The big question always is TX - From who’s point of view?