USB串行通信提供奇怪的输出

Question

I'm trying to get data from a mercury analyzer (Seefelder-Messtechnik Hg Analyzer 3000) that gives output to a 9-pin R232 serial port to my OSX 10.10 laptop.

I've followed the steps described here to install the PL-2303 driver: http://pbxbook.com/other/mac-tty.html

The device manual ( http://www.seefelder-messtechnik.com/V71-3-02-21e.pdf ) lists the communication protocol as "9600 Baud, 8 data bit, 1 stop bit, no log, no parities".

I attempt to read from the device by using the 'screen' command:

screen /dev/tty.usbserial 9600

The result is a string of seemingly non-sensical characters that print to the screen in a regular interval:

8b4 b 8b48bs 8G 8b 8 8 8 < 8 8 b KW \\b 8b b b b KW K 8b \\G < 8 8b " ΁ [؁ ؉ bG 3 ˁ G \\K [W pb 8 ΁8ʱ \\pa ʁ ct 8 h¡ 38b 8 q ؁ \\ 8 bS 8b8 8 q X 8 < £8 2 8 ؖ ؖ ؖ 8bS \\ ܉ ؖ [S 8 s fq 8 8fq S ܊ b b ؉ \\ S K ݎ S b b S S \\ KS S ؊ \\S 1S \\b S ؉ \\ ذ KS \\ S  bS ؉ 1S ؊ [؂ ز ؉\\ ؂ ز \\ i $\\ $ \\ 8 $ \\ \\ ܂ زXk B 7 \\k \\X < 8Xkz Yj L H \\ ]j ،k: Yj ؈

I've also tried using 'minicom' rather than screen, and get a different ("?]???ܰ??Yk??2"), but also non-sensical result. I saw that there was another SO query similar to mine that remains unsolved: weird characters displayed during serial communication OSX

Any tips? It looks to me that I'm not interpreting the output correctly, but I don't know what to try next.

Answer 1

The solution was to read from the machine at a higher baud rate (~57600), despite what the manual and online reference said. Reading at 57600 baud made the result plain-text and usable. Thanks for your ideas!

Answer 2

I've followed the steps described here to install the PL-2303 driver

I've also had occasional electrical ground problems with Prolific USB-RS232 adapters. Problem would manifest as garbled data that looked similar to a baud rate issue or what you posted.

You can check if it's a ground issue by measuring for continuity between the ground pin (pin #5) on the DE-9 (aka DB-9) side of the Prolific adapter and the ground pin of the USB side (pin #4, "far left", of the A connector). You'll probably measure infinite resistance with a multimeter. Try the same with a FTDI USB-RS232 adapter, and instead I get a dead short between the ground pins as expected.

Be sure to plug the instrument's and PC's power supplies into the same power strip.
As a last resort try grounding the instrument's chassis/case with the PC using copper wire