Re: upgrading CBM-3040?

On 11/13/2017 07:48 PM, Francesco Messineo wrote:
> On Mon, Nov 13, 2017 at 7:37 PM, Mike Stein <mhs.stein@gmail.com> wrote:
>>
>> ----- Original Message -----
>> From: "Francesco Messineo" <francesco.messineo@gmail.com>
>> To: <cbm-hackers@musoftware.de>
>> Sent: Monday, November 13, 2017 11:33 AM
>> Subject: Re: upgrading CBM-3040?
>>
>>
>>> On Mon, Nov 13, 2017 at 3:17 PM, william degnan <billdegnan@gmail.com> wrote:
>>>> Yes.  There was an upgrade kit.  If you can find the chips or steal them
>>>> from a 4040 drive here is what I found:
>>>>
>>>> Replace the 6530 with the CBM chip 901466-04
>>>> UL1 gets a 901468-12
>>>> UJ1 gets a 901468-11  (take from 4040 UK1)
>>>> UH1 gets a 901468-13
>>>
>>> ok, the last three chips can be 2532 EPROMs with the right content, no
>>> problems here.
>>> Looking at the schematics, it seems that the 6530's ROM is selected by
>>> /RS0 only, so in theory, I could
>>> make an adapter to tie /RS0 of the original 6530 high, and use the
>>> select signal to enable another external EPROM for the new
>>> code. The rest of the 6530 should continue to work as expected, am I right?
>> ---
>> Some drives use 2332s with an active-high chip enable and it looks like that's the case with the 2/3/4040 drives' CS2, so you might also have to add an inverter in order to use 2532s.
> 
> 
> right.... clock phi2 from the 6502 (buffered) goes to pin21 of all the
> ROMs. It prevents the ROMs to be selected during the low part of phi2.
> Now I'm puzzled, what would drive the data bus during the low part of
> phi2 that they had to prevent a possible bus conflict?

I thought the dual drives use a dual CPU setup with shared RAM and one 
of the 6502s run on an inverted clock signal so that one 6502 uses one 
half of the cycle and the other one the other half.

Using Phi2 way you make sure the ROMs are only visible to the CPU that 
uses them but invisible to the other.

  Gerrit


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