Re: 6x0x board with dual CPU installed?

[oscarv <vermeul...@gmail.com>]

Hmm. Response to self:

Not so easy. "But a normal 6502, even stopped, still drives all the lines and that is not acceptable for the VIC so the developers of the 6510 built a feature inside this chip which made it possible for the VIC chip to tell the 6510 to disconnect itself from the bus. The name of the input for the 6510, which performs this function: AEC."

That makes the question more complex (HALT/RDY is not enough)- but still: is it feasible to select from two installed CPUs?



Regards,

Oscar.


On Monday, September 3, 2012 10:48:08 AM UTC+2, oscarv wrote:
> Hi,
>
> I'm in the process of building my ECB 6x0x boards (Processor & Mezzanine). Although my aim was to play with Cubix, I would like to experience DOS/65 as well.
>
> The point is, the 6x0x board was set up to give you the choice of CPU 'at build time'. But what is necessary to actually install both CPUs on the board, using front panel switches to disable one or the other CPU? I just like to maximise the bells-and-whistles count on my N8VEM...
>
> As far as I can see from studying the schematics,
> 1 - of course, jumper settings need to be switched before boot-up
> 2 - the CPU that's not in use needs to be truly off-line
> 3 - the ROM needs a 6809 and a 6502 boot image
>
> On 1, that's clear.
>
> On 2, is it enough to cut two traces, install switches and use them to pull down the /HALT line on the CPU you want to disable? I should really study before asking, but I guess others have thought of this before.
>
> On 3, I believe the board can hold a 2732 instead of a 2716. The pinout when not programming them is only different on pin 21. So, lift out pin 21 (which is A11 for 2732/Vpp for 2716), and pull it high/low with a front-panel switch to choose whichever 2K image.
>
> I really look forward to bringing up the 6x0x boards - they are a really nice extension of the N8VEM platform and somehow, I missed out on the fun when they came out!
>
> Regards,
>
> Oscar.
>