I had something like that 30 years ago on a Motorolla 68332 processor. It could generate the high speed CPU clock using the 32khz clock as a reference. What I

I had something like that 30 years ago on a Motorolla 68332 processor. It could generate the high speed CPU clock using the 32khz clock as a reference. What I found was the layout guy ran a digital trace through the pins of the 32khz xtal. There was enough coupling that digital transitions on that line would cause the high speed clock to swing wildly. Which showed up as garbage on the UARTs. Joyous thing is most of the time that line was idle. I cut and rerouted the trace and the problem went away.