Date : Mon, 06 Oct 2008 21:19:32 +0100
From : jumbos.bazzar@... (Mark Haysman)
Subject: New 6502 second processors?
Hi.
It's something I almost started a few months ago. I had 2 projects I wanted
to get done, a remake of the 1770 DFS PCB, and a 6502 Co-Pro. I've done the
1770 board, and sourced some VL1772s from the states. For the Co-Pro, I got
all the info I needed ready, and started scribbling about remaking the ULA,
but just got sidetracked.
I was going down Michael's route, use a CPLD for the ULA and associated
logic, then have static RAM, EPROM, etc, and a 65SC102 CPU. It would depend
on sourcing a good quantity of the CPUs, and fitting it all into cost
effective all round solution. I'm all for breadboarding stuff up for the fun
of it, but if you have to make the expendature of having PCBs made, and
buying obsolete ICs in quantity from a vendor, then it needs to be something
that's sellable at the right price to recover some costs. I would have
thought using an FPGA would push the cost up too high, although it would
allow a faster speed I suppose.
If anyone has VHDL or a schematic of the ULA already done, I'd be interested
in taking a look.
Mark.
----- Original Message -----
From: "Phil Blundell" <philb@...>
To: "Michael Firth" <mfirth@...>
Cc: <bbc-micro@...>
Sent: Monday, October 06, 2008 8:45 PM
Subject: Re: [BBC-Micro] New 6502 second processors?
> On Mon, 2008-10-06 at 20:14 +0100, Michael Firth wrote:
>> Has anyone given any thought to producing replacement internal or
>> external 6502 second processors?
>
> I did think about this at one point, and I actually got as far as
> building some PCBs with the appropriate circuitry on. The idea was to
> put the 6502 plus ULA emulation into a single FPGA - some kind of
> Spartan-3 if I remember correctly, clocked at somewhere around 40MHz.
> Aside from that you just needed an external SRAM, an EPROM, some bus
> level translators and the power supply circuitry. I think I also ended
> up having to use a small XC9500 PLD to load the image into the FPGA, for
> reasons which escape me at present.
>
> Annoyingly though it turned out that I had gotten the PLD pinout
> hopelessly wrong: I had somehow laid the board out for a TQFP device but
> used the pin assignments from the PLCC part, or vice versa. In any case
> it would have required an inordinate amount of fiddly hand-wiring to
> make the device fit, and I don't think I ever had the patience to do
> that.
>
> That was a couple of years ago now, and I suspect most of the parts I
> used at the time are probably discontinued. I'm pretty sure the RAM, in
> particular, is impossible to buy now. I keep thinking about having
> another crack at that project but it would probably need to be more or
> less redesigned from the ground up.
>
> p.
>
>
>
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