NoCan(x) Auto-Refresh Waveforms

This is a 'scope photo showing the auto-refreshing waveforms. Between the two vertical lines are the auto-refresh parts of the waveforms. This portion is during non-cpu time (video time, because the signal HSync is at a logic low) and only during HSync or VSync time. Between the vertical lines, video is not occuring, so refresh is done then automatically by swapping RAS for CAS at the SIMMs. This forces the SIMMs to do internal auto-refresh by themselves. Just to the right of the second vertical line is the CPU access, notice E is high. After HSync goes high, the next video access (go past E, where E is low) is a normal video access. Notice that RAS and CAS have normal widths, just like the CPU accesses. When this photo was taken, this CoCo-3 was running at double speed, 1.79MHz. These waveforms (were measured on the second version of RamZilla and) are identical to NoCan's style of refreshing.