Re: General 6809 card for 6502 machines

Den Thu, 19 Oct 2017 22:28:10 +0200 skrev didier derny
<didier@aida.org>:
> the liber809 is built specially for the atari 800xl  (and some other 
> similar)
> 
> the 6502 used on atari is not the standard one   3 pins are differents
> RW is not on pin 34 but on pin  36  (on sally  34 is NC)
> there is a HALT signal on pin 35  (nc on a 6502)
> the clock used on the atari is 1.75Mhz   (not 1mhz)
> 
> to produce Q  the liber809 is using a digital delay line  calculated
> for a 1.75Mhz
> so if your clock is 1Mhz Q arrives too late

Woudn't it rather arrive early?

I.e. to delay 1,75MHz one quarter cycle you would have a delay of about
143 ns but for 1MHz it would be 250 ns. With 143ns at 1MHz the four
phases of the 6809 clock would not be equally long, but each would be
within spec for the timing requirements for the 6809.
 
> in the past I had a project to put a 6809 on a 6502 socket
> or a 6512 on a 6809 socket :)
> but never had time
> 
> I'm trying to check on how I could make that type of adaptors but 
> compatible with several clocks

A PLL would probably be the only way if you want to be able to use a
1MHz 6809 in a 1MHz 6502 machine and with the same hardware use a
faster 6809 in a equally faster 6502 machine. But it takes some time
for a PLL to synchronise to it's clock so it might not work in a
application which switches speed like for example the C128.

But how many different 6502 machines could this be relevant for? As
there is already the liber809 for Atari we could perhaps ignore Atari.
That probably leaves us with many machines running at about 1MHz, some
running at 2MHz (C128 if we emulate $0/$1) and also the BBC computer. I
don't know of any computers with 6502 that runs faster than 2MHz, but I
haven't looked for them.

Another way to see it is which speeds 6809's are available at, and just
make the delay fit each possible CPU speed. By looking at Wikipedia the
Motorola 6809 were made for 1 and 2 MHz while Hitachi 6309 were made in
another version running at 3,58MHz (and according to Wikipedia usually
possible to overclock to 5MHz).

Someone needs to read the data sheet to see if I'm making a correct
guess that the phases don't have to be equally long. If the as I
suspect don't, then the hardware could just be set for the kind of CPU
that's inserted, using a jumper, and then working fine at any clock
frequency that the specific CPU can handle.

It seems like standard 6502's were made for 1, 2 and 3MHz while the
65C02 can run up to 14 (!) MHz. So it's a question of which speeds to
support.

-- 
(\_/) Copy the bunny to your mails to help
(O.o) him achieve world domination.
(> <) Come join the dark side.
/_|_\ We have cookies.

       Message was sent through the cbm-hackers mailing list