First, just to say, I've been lurking here for far too long I'll try to make an effort to post more often... So hello to those who don't know me from other forums.

Crystal oscillators using logic gates back then, was one of those areas of electronics that was known in some circles as a "black art" (hard to understand, so left to the people who were 'good' at it). So data sheet designs would often be copied.

I think the older MOS circuits are created to minimize the amount of glue logic. In 1975 each gate was valuable

Might be worth noting that these days clock cans are much preferred - they are encapsulated oscillators, literally.

Congratulations!

May I asked how many inverters/buffers you have left in your oscillator circuit?

Hello,

I'm working on a work-alike build of an Acorn System 1, which had an NMOS 6502 running at 1MHz. I've got a fistfull of Rockwell 6502s to hand, but the 1MHz crystal was a bit more bother. It seems they only exist in the big HC-51 package, which is too big for my board, so I'm planning on using an 8-pin DIP oscillator instead.

Attached is an extract of the System 1's circuit diagram:


(As can be seen, the System 1 supported using a capacitor instead of a crystal for industrial applications where timing was not critical.)

I'll be connecting the DIP oscillator directly to Phi0in, and removing the resistor and crystal/capacitor. That'll leave me with Phi2out passing through a pair of inverters on its way to fee the rest of the board. Are the inverters needed? The only benefit I can foresee is that using the 74LS04 to drive the board's clock may be preferable to using the 6502, and that there are two extra gate delays on the Phi2 clock. If these weren't needed, why wouldn't the designers have taken Phi2 direct from the 6502 and foregone the second inverter? Or would this mean the other devices connected to Phi2 would affect the crystal's timing?

Looking at Garth Wilson's primer on clock generation, he suggests a different crystal-based circuit, where Phi2 goes directly to the board, and isn't used in the clock generation. (This is the style of circuit used by Acorn in their later BBC Microcomputer.) This suggests that the double-inversion isn't needed in my case.

If the two inverters are no longer necessary, I may repurpose them for something else.

Hi,

Did you ever complete the project? I have yet to start!!

viewtopic.php?f=12&t=3286&hilit=planning+build+acorn#