Just a silly quick question. I am putting together a board that has a ATMega328 and ATTiny45 and uses a 20MHz Crystal, I only have Mica caps. Would these work or should I stick with Ceramic Caps?

 

hi Leland,
Welcome to AAC.
I would use either of those two types, what value pF do you have in mind.?
E

 

The BOM is calling for two 18pF.
I'm building this for a Z80 Retro Computer I am planning to start building.

 

hi,
That cap value is OK.
Are you using an actual Z80 as the processor with a 20MHz xtal.????

E

 

No, Haven't started on the Z80 Computer yet. Just building a TTL VT100 compatible Video board to use an old Analog Scope as the Monitor for more of the old school baremetal feel. A matter of fact I have parts from an old Heathkit Scope that I could cobble together a basic XYZ Monitor. Granted I can just use my Linux box with a TTY session but it's been done to death. Down the road I can attempt to make it run some Vector Graphics.

For the Z80 Computer it will have real vintage parts and probably be around 8MHz or 10MHz. Debating to use the Zilog KIO chip instead of using separate PIO, SIO and CTC chips. The end result specs would have 64KB RAM, Compact Flash for storage and run CP/M or some variant flavor of UNIX. Probably end up building it on a Blackplane and build daughter boards for everything for easy modifications and additions.

 

hi,
I used a 6MHz xtal with my Z80 based products, look at the Z84C90 peripheral IC, very versatile.

Are you based in the UK.?

E

 

Yep, that's the same KIO I was thinking of, didn't remember the model number off hand.
I know the RC2014 runs at almost 8MHz. I got some Z80s laying around that can handle 10MHz. I was thinking to have a board with some circuitry to divide the clock speed with some switches so I can change the clock speeds for certain applications. If I plan to run UNIX on it I would like to go 10MHz or even higher if possible but if I run UNIX then I would need more then 64KB of RAM.

I came across this in my bookmarks for building a simple XYZ scope. I got a 5UP1 CRT from a Heathkit Scope but it may be too small for ASCII text. Might just buy a cheap XY Monitor or just stick with my 30MHz Analog Scope.

I'm in the States, Florida.

 

hi,
That's a very basic scope, as you say a cheap monitor would be a better bet.
You could consider a USB/PC scope for general purpose use.
Lets know how the build goes.
E

 

Yep, that's the same KIO I was thinking of, didn't remember the model number off hand.
I know the RC2014 runs at almost 8MHz. I got some Z80s laying around that can handle 10MHz. I was thinking to have a board with some circuitry to divide the clock speed with some switches so I can change the clock speeds for certain applications. If I plan to run UNIX on it I would like to go 10MHz or even higher if possible but if I run UNIX then I would need more then 64KB of RAM.

I came across this in my bookmarks for building a simple XYZ scope. I got a 5UP1 CRT from a Heathkit Scope but it may be too small for ASCII text. Might just buy a cheap XY Monitor or just stick with my 30MHz Analog Scope.

I'm in the States, Florida.

What UNIX hack are you planning to run? Something like this?
http://uzix.sourceforge.net/
https://github.com/EtchedPixels/FUZIX

 

Mica caps are more expensive than ceramic caps. Either will work. For less stray inductance, use ceramic chips - you'll get a more accurate clock (if that really matters). Chips are far more accurate than leaded devices, are smaller and easier to route to.

 

hhmm, I do have a HP 16500C that I have my main Linux Box able to display the video with some X11 trickery but I don't know if the Scope has a XY Mode.

As for the flavor of UNIX to run with the Z80 I haven't put that much thought into it yet. Might give both UZIX and FUZIX a spin.

Yea, Mica is way more expensive but I have a lot of Mica caps from when I was giving Tube Radio restoring a try so I thought maybe if Mica works well for RF Coils and Oscillators I would think it should work with a Crystal Oscillator but wanted to make sure before I wrecked something.