I've seen two parallel SPI tracks on one side of a PCB cause chirps in a stereo audio track on the opposite side of the PCB which was routed perpendicular to the SPI tracks. No ground was near the SPI tracks. The solution was to put a wire on top of the SPI tracks between the clock and MOSI pins (there was no SIMO track) and solder both ends to of the wire to ground. No chirp was ever heard again on the audio output.

I'd expect the SPI to cause problems with the UART, but not the other way. You should use an osciloscope to find out what happens on the SPI line when you send data on UART, but I think it might rather be a software problem. More details about the hardware and application, and the relevant code would be helpful.

Regards,
Michael K.

--- In m...@yahoogroups.com, "merapcb" wrote:
> I have a UART device who's lines intersect the SPI lines going to another device. When the UART sends data, the SPI device fails. Can it be that the UART lines are generating interference? (UART is at 19,200 and SPI is at 3MBps)
>
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