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Speed and components

The slowest component will set the speed of the computer, hence the need for picking the right kind.

CMOS 40xx series, for examples, are too slow, with propagation delays in the order of 100 ns. This is slower that most static RAM chips. HCMOS chips, in contrast, are very fast with propagation delays some times less than 10 ns (6 ns for 74HC00).

For registers, 74C374 gives me 165 ns from clock to latch. In contrast, 74HC374 gives me 20 ns. Same access time (20 ns) is found in SRAM 32Kx8 chip CY7C199CN from Cypress; I would use that chip for building the "Matrix" which is part of the CPU. 74LS series is even faster, but it is also more expensive; for my purposes, HC is OK.

As per PLDs, they are very fast. Amtel ATF22V10C for example (a good candidate for the Heritage/1) doesn't have any figure greater than 10 ns. Time from clock to output, for example, is 2 ns.

It seems then that the interval between control signals can be set around 20 ns. This makes a clock speed of 50 MHz, which is an impressive figure (I was thinking of 12 MHz before) but it's too early for making decisions about clock speed because no circuit have been designed yet. I just wanted to run some numbers and see where they would take me.

What is clear is that CMOS 40xx series are not use, so I shall employ HCMOS components instead.