Help! ..no TTL oscilator available...

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Joined: Apr 27 2005
Posts: 9

I bought all the parts for the Replica I
and designed my own board (actually I'm using PICs, I know them better)

The one part I couldn't buy here in Mexico was the 1Mhz TTL oscilator...
I know a little bit of electronics, but haven't tought how to build one,
any sugestions?

With The PIC I'm working on a Color signal generator for the TV,
I think it would be quite useful

Thanks,
Leopoldo

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Offline
Joined: May 24 2005
Posts: 41
Re: Help! ..no TTL oscilator available...

Maybe you could try to choose another higher value and make a frequency divider..

Or buy that via internet

Offline
Joined: May 24 2005
Posts: 41
me again

ey look what "leopoldo" says at "got the book today" discussion. Maybe you'll have an answer

regards, Luis

Offline
Joined: May 24 2005
Posts: 41
oops

ooops you're leopoldo sorry!!

Offline
Joined: Apr 27 2005
Posts: 9
ahha :-)

Hi,

yes, at first it seemed to work but the signal doesnt oscillate
good enough...

It looks like this /````----_____/````----_____

The 6502 tends to freeze randomly, I tried also to use a smitt
trigger version, but then theres a strange effect, the low state
is longer than the High state.

There must be a way to do it, also you need an osciloscope to test
that, I currently use my soundcard, but it's far slower...

What is the maximum Mhz allowed for the 6502?

moros's picture
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Joined: Jan 21 2005
Posts: 65
You could try...

You could try looking at http://www.6502.org they have a lot of pages with tech info etc. on them. One of the guides uses a 555 timer to produce pulses.

IIRC the 6502 comes in several speeds, the BBC Micro uses a 1MHz version but I think the max is around 10MHz.

Hope this helps!!

Joel

Tom Owad's picture
Offline
Joined: Dec 16 2003
Posts: 2460
The original Apple I didn't u

The original Apple I didn't use a TTL clock. See the original processor section schematic if you'd like to use transistors and capacitors.

Here's a page on designing oscillators.

(I can't imagine it wouldn't be easier to order one from the U.S. though.)

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Offline
Joined: Apr 27 2005
Posts: 9
Yes, I realize that now :-)

I somehow managed to make a more or less ok
2Mhz signal, the next part is to divide it by 2...
that's easier, I'll try it, if it works, then
I publish it here Smile

Indeed it's too expensive to buy just one part from the US,
shipping is usually above 6US... hahaah

In the other hand, "I can get no satisfaction"
(without some sacrifice ahahha, specialized electronics is rare)

Offline
Joined: Apr 27 2005
Posts: 9
Wonderful Square Waves :-) 1Mhz and more :-)

Finally, there's a great solution...

I managed to program a PIC to make 1Mhz PWM with 50% cycle,
but changing 2 jumpers you can change the speed, that's great,
because you can change CPUs with diferent speeds easily Laughing out loud

Schematics & firmware comming soon.