1202 wrote:
I now believe there is a problem mixing digital logic with say the crystal of the analogue world of spice!! I'm using circuit maker 2000 but I also have access to ewb and microcap, anybody have any help on this!!
interesting but fustrating as I wanted to simulate a clock for a 6502 using digital logic and a crystal! now I can't see how I'm going to do that...
SPICE is a simulation tool designed to simulate
integrated circuits (the IC part of SPICE), both analog and digital alike. SPICE works by emulating individual components and their basic operation according to various models. SPICE isn't a 100% perfect simulation, of course, but it's often considered good enough. After all, the whole integrated circuit industry grew up around it.
That being said, SPICE can't possibly be applied to macroscopic circuits; not, at least, without some really funky measures taken. This is because SPICE can't fathom inter-trace capacitances and lead inductance in real-time. It has no idea of how the physical geometry of a circuit would affect operation, etc. All these factors are actually quite important in getting a circuit working as desired,
especially oscillators. In the amateur radio community, at least, there's an old truism: oscillators amplify, and amplifiers oscillate. You might be running into this problem. I'm not quite sure.
I've created circuits that I know would work in the real-world, but which patently didn't work at all in SPICE. For example, a doubly-balanced diode mixer will not simulate in the SPICE packages I've used.
It's been too long since I last used SPICE to tell you how to do it. But I've seen it done before. Maybe you should ask on some of the electronics-related newsgroups? I'm sure someone there would be able to offer assistance for this.
Just a suggestion.
Also, SPICE has built-in "ideal" clock waveform generation built-in. Might that work as well?