Nice, Garth -- I like how the duration of the 245's enable time is curtailed by the NAND pulse-shrinking circuit. That gives a bit of dead time to serve as a timing cushion and prevent bus contention between the 816 and the '245. But, as you know, a too-generous cushion will cause you to fall short of the 816's true performance potential, and that's where the variable delays come in. (I realize your diagram omits the variable delays units.)
If it's to be a quest for absolute max performance, I assume you'll also provide a means to experiment with clock duty cycles other than 50%. It'd be no surprise if actual (rather than documented) minimum pulse-width for Phase2
low differs somewhat from the actual minimum pulse-width for Phase2
high. Only experimentation will reveal this. Perhaps your clock oscillator should be made of two variable-delay units connected nose-to-tail in a loop.
One delay unit would determine the Phase2-high time and the other'd set the Phase2-low time. (You'd need an inverter in the loop, too, but I'm sure you get the idea.)
Also on the absolute max performance checklist, remember to consider a FET bus switch such as
74bct3245 as a drop-in replacement for the '245. That'd be a tradeoff. The device has near-zero prop delay, which gains you some speed, but the gain would be reduced (or in a large system even reversed) by capacitive loading, which a FET bus switch won't buffer.
A FET bus switch could also be considered as a faster replacement for the '573 bank-address latch. We discussed this privately -- allowing the RAM address inputs to dynamically hold their state via capacitance. Pinout-wise you'd have to finagle things slightly but the '573 and 'bct3245 are both arranged 8-bits broadside, so it'd be doable -- especially if you're using one of these
adapters to place the SOIC bus switch IC on a .1" grid.
-- Jeff
ps to BDD - I think the main obstacles to photographing an oscilloscope screen can be overcome with just some patience, a tripod, and a means to avoid
reflections. This means keeping the camera and any other reflected-view objects in the dark or obscured from sight. A hood would do the trick... or we could take a masterful tip from Ford Prefect and use a
towel!
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