Any luck with a Serial Cable?

[acid andy]

I'm trying to diagnose an issue stopping a distro on my PinePhone from booting (with U-boot).

I bought a serial cable but when I connect it to my Linux desktop PC, I get a load of garbage characters and no readable text at all. It's a nightmare!

I started off with the recommended settings I've found on this site and elsewhere: 115200 8N1. When this just gave me garbage I tried just about every baud rate available and even different values for the data bits and parity. The output would change but never became readable text!

I'm not using USB, it's a 3.5mm headphone plug to RS232 and I had to add a null modem (crossover) adapter, connected to my PC's RS232 port, which is read using /dev/ttyS0.

Has anyone else had a similar problem? Or does anyone even get any readable serial output from their PinePhone using a recent U-boot?

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Argh! Looking around it sounds like an RS232 port may use too high a voltage for the PinePhone's 3.3v TTL serial connection! Maybe time to order a cable that plugs into USB instead, if I haven't fried part of my PinePhone.  

https://forum.pine64.org/showthread.php?tid=8378

[8bit]

RS232 uses inverted signals, probably why you are getting garbage. Some computers use lower voltages on the RS232 port, but not a good idea to directly interface it with a device expecting 3.3v signals.

[acid andy]

RS232 uses inverted signals, probably why you are getting garbage. Some computers use lower voltages on the RS232 port, but not a good idea to directly interface it with a device expecting 3.3v signals.

Ah thanks, that makes sense. I've taken wire cutters to my cable and I'm going to connect it to the GPIO pins on my Pi instead.

[acid andy]

My bodged cable worked
Onto the next problem...