I’m not done with overclock testing since it hasn’t failed yet. The RAM I’m using is 25nS part which is really too slow for 30+mhz operation. I need to swap in a 10nS RAM. I’m actually surprised that dynamically changing clock worked, all that worries about fractional clock phase or glitches in clock output do not appear to a problem, then again I need to run the tests repeatedly to be sure. Changing clock is a different way of working with slow peripherals; maybe there are applications for this approach. Alternatively I can use a 22V10 as a fast bootstrap ROM, add a CF interface such that 22V10 ROM loads and runs programs from CF disk.
Bill
I'm not so surprised, as the DS1086 should guarantee that, although I didn't check the datasheet - but from what I remember it does guarantee things like not outputting any signal on power-up until it is able to output the stable oscillating signal that you've programmed it for, so it ought to also be able to guarantee that frequency changes happen without for example generating short pulses in the transition. It's a nice little device - I used one too, and also made an adaptor board to fit it into the corner pins of a DIP-8 socket.
It is interesting to see that the 65C22 does work at those speeds, and I wonder whether there's an existing test suite that can be used to more thoroughly validate all the functionality. I know that with the 65C02 it can sometimes appear to be stable though fail something like the Dormann tests. It would be hard to properly validate that for a 65C22 though because some of the validation would need to be done by external hardware.
It would be good to kick the tyres a bit more though on things like the shift register and externally-triggered interrupts to make sure those things are also OK. Shift register I/O at >30MHz would be great for a lot of things, e.g. faster reads from SD cards if the card can also keep up.
That was my thought regarding W65C51N6TPG-14; I thought it is .6u thus capable of much higher clock, at least to 14mhz, but I could hardly get it run faster than 7.37mhz. W65C22 turns out to be more like W65C02. It is also a more powerful peripheral, so much the better.
I wonder whether the 65C22N also works at these clock speeds, perhaps there is a difference in the process for "N" devices that means they don't scale as well.
