I've seen several places where a 74xx75 is used as clock divider.

There is no need of set/reset signals, as it's a D-type latch.

I want to divide DOTCLOCK (~8Mhz) from the C64 Expansion Port, to feed a w65c265s' FCLK (fast clock) input with half that clock speed.

The circuit would be like this:


Any experience or recommendation of a better solution?

Thanks.

Hello! I guess it depends on what you want to optimize for… from the datasheet, it looks like the '75 would work fine in a C64, but (a) you would end up with a bunch of unused gates, and (b) it's quite expensive (Digikey lists it at $3.50 CAD).

If these things don't matter, I wouldn't overthink it, especially for a single prototype… just wire one up and see if it does what you need. You can always go back and change things around, especially if you find that another configuration gives you some advantage that you discover at a later point.

There are a bunch of alternatives, again depending on what you want to do. You could use a counter (like, say, an 'HCT161), which is cheaper (~$1) and will give you other clock divisions (/4, /8, /16), for example.

Thank you very much. So a counter then, will do it. I'll take a look on that.

I just want to halve the clock coming from the C64 and have ~4Mhz, because ~8mhz is too much by now, and ~1mhz coming from PHI2 is maybe not enough, at least for FCLK (fast clock).

A counter (such as a '161) is good choice. The '75 is not, as it's a transparent latch (ie, follow-hold operation, like a '373; not an edge-triggered, like a '374).

-- Jeff

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

My deepest apologies, I was thinking about the '74. Sorry for the snafu (and thanks, Jeff).

Thank you very much both of you.

I maybe too late, but I would suggest a 74LS93. It's a small package (14-pin) and will give you /2, /4, /8. /16. The other 3 divisions you can use for whatever.

Just be careful as the Vcc and Gnd pins are in odd places.

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Bill