UART Noise ?

Hi Folks,

Hoping someone can point me in the right direction - and apologies for not being much of an EE !

Currently trying to get access to my car head unit - long story short, I can see data fine using a logic analyser and pulseview but get absolute garbage when using either ft232rl, cp2102 or even a max3232.

Pulseview uart decoder set to 9600 8n1 no parity, not inverted and lsb first - about as standard as it comes.

Looking closely in pulseview I seem to be getting erroneous "spikes", seemingly not enough to generate any frame errors or misinterpreted breaks - but still, doesn't look right.

Or am I going completely the wrong route here?

Any ideas much appreciated!

Try looking for noise with an oscilloscope, not a logic analyzer.


Yes a LA can hide a multitude of problems such as interference, slow edges, wrong voltages, etc etc.
Vehicles are particularly bad for noise spikes, due to the ignition and all the electric motors sharing
the same wiring harness.

Clearly there are short noise spikes present, which needs sorting out - I would worry about the
voltage peaks being over the abs max for the chip you will use to decode the serial, as well as causing
occasional corruption.

Thanks for the fast replies!

Unfortunately I don't have an oscilloscope in my array of tools (yet).

I did suspect that the LA would "hide" some of the issues afoot - but was glad the see plaintext nonetheless.

I rummaged through my box of toys and found my opto isolated ft232rl (probably should have started with this one...) and I do now atleast get clean uart output.

XTP_Cache( )
XTP_DramBank( )
XTP_DramAddr( )
XTP_DramBit( )
XTP_DramRef( )
XTP_RamBacc( )
XTP_RamWacc( )
XTP_RamBacc2( )
XTP_WD1( )
XTP_WD2( )


 Hit any key:

However TX is seemingly ignored - so I suspect something still not quite right.