shirsch
Veteran Member
My Heath H-11 is fitted with a quad-height M7264 LSI-11 CPU board holding 4k words of memory. It's operational and passes all the xxdp diagnostics. While troubleshooting issues that appear with Q-Bone in the system I discovered a very noisy BIRQ7 signal on the backplane (see scope photo below). While this causes no problems with the CPU (it's simply dead-end terminated on the board), the bigger question is what's causing it. There were no other boards in the system at the time that trace was grabbed. The +5 supply rail is quite clean (see scope photo) and ground is equally so. Since there is nothing driving the BIRQ7 line where in blazes are these spikes coming from? I have verified that both termination resistors are showing correct values. Anyone have thoughts?