CBM-II solderless memory expansion

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CBM-II solderless memory expansion

Michał Pleban
Hello!

The widely known method of expanding a CBM-II memory requires soldering
several things on the motherboard, which is doable but not for the faint
of the heart.

Alternatively you can also use the expansion port to connect a big SRAM
chip which could expand the memory for the 6509, but it would not be
seen by the 8088 card.

So I thought about an easier way to expand the memory. The standard
method uses 41256 chips instead of 4164. But how about using 4464
instead of 4164? The memory banks would still be 64kB in size, which
means that all that is needed is a custom PLA; PLA is socketed on most
motherboards so it could be a straightforward expansion.

Just to test the waters, I replaced a row of 4164's today with two
4464's and it works fine. Did anybody go down this route before?

Regards,
Michau.

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RE: CBM-II solderless memory expansion

Baltissen, GJPAA (Ruud)
Hallo Michał,


> But how about using 4464 instead of 4164? The memory banks would still be 64kB in size, which means that all that is needed is a custom PLA

I think we miss a bit of info which is obvious for you. My question: how are you going to select the extra banks?

I have some more questions but I have to study the SCH first.

FYI: I'm always willing to help you with a PCB again :)


Met vriendelijke groet / With kind regards, Ruud Baltissen

www.Baltissen.org




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Re: CBM-II solderless memory expansion

Michał Pleban
Hello!

Baltissen, GJPAA (Ruud) wrote:

> I think we miss a bit of info which is obvious for you. My question: how are you going to select the extra banks?

With a custom PLA. Currently the PLA is generating RAS/CAS signals for
the four 64kB banks that are on the mainboard. Since the PLA equations
are now known, a GAL can be programmed to generate RAS/CAS signals for
the remaining banks.

Regards,
Michau.

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Re: CBM-II solderless memory expansion

Gerrit Heitsch
In reply to this post by Michał Pleban
On 04/12/2018 10:05 PM, Michał Pleban wrote:

> Hello!
>
> The widely known method of expanding a CBM-II memory requires soldering
> several things on the motherboard, which is doable but not for the faint
> of the heart.
>
> Alternatively you can also use the expansion port to connect a big SRAM
> chip which could expand the memory for the 6509, but it would not be
> seen by the 8088 card.
>
> So I thought about an easier way to expand the memory. The standard
> method uses 41256 chips instead of 4164. But how about using 4464
> instead of 4164? The memory banks would still be 64kB in size, which
> means that all that is needed is a custom PLA; PLA is socketed on most
> motherboards so it could be a straightforward expansion.
>
> Just to test the waters, I replaced a row of 4164's today with two
> 4464's and it works fine. Did anybody go down this route before?

A 4464 cannot be put in place of a 4164, so I don't quite see how to
make that 'solderless'... Could you provide a bit more detail?

  Gerit


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Re: CBM-II solderless memory expansion

Michał Pleban
Hello!

Gerrit Heitsch wrote:

> A 4464 cannot be put in place of a 4164, so I don't quite see how to
> make that 'solderless'... Could you provide a bit more detail?

The high-profile board has 128 kB soldeded and sockets for additional
128 kB RAM. The board with 4464's would go into these sockets.

Regards,
Michau.


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Re: CBM-II solderless memory expansion

Michał Pleban
In reply to this post by Baltissen, GJPAA (Ruud)
Hello!

Baltissen, GJPAA (Ruud) wrote:

> FYI: I'm always willing to help you with a PCB again :)

Gladly :-) But I think I need to draw the schematic first (which I neve
did before). Do you possibly have a 82S100 symbol for Eagle?

Regards,
Michau.


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Re: CBM-II solderless memory expansion

MiaM
In reply to this post by Michał Pleban
Den Fri, 13 Apr 2018 17:46:27 +0200 skrev Michał Pleban
<[hidden email]>:
> Hello!
>
> Gerrit Heitsch wrote:
>
> > A 4464 cannot be put in place of a 4164, so I don't quite see how to
> > make that 'solderless'... Could you provide a bit more detail?
>
> The high-profile board has 128 kB soldeded and sockets for additional
> 128 kB RAM. The board with 4464's would go into these sockets.

You might aswell go for 41256 or 44256 then. 128k soldered on to the
motherboard for bank 1 and 2, 3 sets of either 8 41256 or 3 sets of 2
44256 will fill 12 additional ram banks, i.e. bank 3-14.

I don't know if there is any reason to fill bank 0 aswell. It might be
a good idea to use 1mbit 1 bit wide (or 4mbit 4 bit wide, or an 1MB 30
pin simm) to fill all of bank 0-14.

With some additional patches to the motherboard it could be possible to
fill the parts of bank 15 that's emtpy in an unexpanded machine aswell.
That patches could be included in a 6509 replacement board.

To be able to produce something at all without my usual terrible
feature creep, just leave some inputs to a GAL/CPLD connected to some
pull-up resistors and a pin header (or a pin header which can hold
jumpers while not being used for some "bank 15" add-on).

With a circuit using an 1MB simm or 1mbit/4mbit dram chips it would
also be a repair for machines with broken on-board DRAMs.

So, there would be two PCB's. One that sits on top of the ram sockets
and holds some other kind of ram. I'd suggest making layouts for both
30 pin simms and for different types of dram. Even if there will be
no shortage of some specific type of dram, it would be nice to be able
to use what's at hand. And then there would be a PCB that sits in the
relevant PLA socket.


P.S. there is another way of doing this, and that involves an
additional set of MUXes and some card that both sits in the expansion
socket and the coprocessor socket, and mimics what the muxes does on
the motherboard. With fast enough sram instead of dram it might be
possible to let the 650x and the 8088 have access to that memory almost
simultaneously, i.e. the software sees memory from both CPU's but in
practice the accesses of course takes place sequentially. Unfortunitely
the 8088 board is clocked on it's own 15MHz oscillator. This would be
more feasable if the 8088 used the same oscillator as the rest of the
computer. By looking at the schematics and at the 8284 clock generator
it seems like the 8284 could easily be replaced with a 74xx74, the
existing timing generation on the B motherboard and maybe some simple
gates. The 8284 can do a bunch of things with the timing for an 8088,
but in a B machine it seems like it only divides the oscillator with 3
and makes sure that the reset and ready signals are synchronized to the
clock signal. If the motherboard oscillator would be used, the 8088
would run at 6MHz instead of 5MHz. Maybe some circuit doing this could
be added to an updated 8088 card replica. But this is my usual feature
creep :)


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

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Re: CBM-II solderless memory expansion

Michał Pleban
Hello!

Mia Magnusson wrote:

> You might aswell go for 41256 or 44256 then.

Then you have to solder additional address multiplexers on the
motherboard, which is exactly what I want to avoid.

> P.S. there is another way of doing this, and that involves an
> additional set of MUXes and some card that both sits in the expansion
> socket and the coprocessor socket, and mimics what the muxes does on
> the motherboard.

Yes, there is a possibility I am thinking about too.

Regards,
Michau.

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Re: CBM-II solderless memory expansion

Gerrit Heitsch
In reply to this post by MiaM
On 04/13/2018 09:10 PM, Mia Magnusson wrote:

> Den Fri, 13 Apr 2018 17:46:27 +0200 skrev Michał Pleban
> <[hidden email]>:
>> Hello!
>>
>> Gerrit Heitsch wrote:
>>
>>> A 4464 cannot be put in place of a 4164, so I don't quite see how to
>>> make that 'solderless'... Could you provide a bit more detail?
>>
>> The high-profile board has 128 kB soldeded and sockets for additional
>> 128 kB RAM. The board with 4464's would go into these sockets.
>
> You might aswell go for 41256 or 44256 then.

44256 need more refresh... 41256 and 4464 use 8 Bit refresh, just like
most 4164, but the 44256 need a 9 Bit refresh which you will have to
generate in some way or you will lose data.

  Gerrit




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Re: CBM-II solderless memory expansion

MiaM
In reply to this post by Michał Pleban
Den Fri, 13 Apr 2018 21:48:53 +0200 skrev Michał Pleban
<[hidden email]>:
> Hello!
>
> Mia Magnusson wrote:
>
> > You might aswell go for 41256 or 44256 then.
>
> Then you have to solder additional address multiplexers on the
> motherboard, which is exactly what I want to avoid.

You could place those on a pcb in the PLA socket.

Either way you'd still need some wires between a PLA replacement and
something that you plug in the RAM sockets, so there is no big
difference here, just different firmware for a GAL/CPLD.

> > P.S. there is another way of doing this, and that involves an
> > additional set of MUXes and some card that both sits in the
> > expansion socket and the coprocessor socket, and mimics what the
> > muxes does on the motherboard.
>
> Yes, there is a possibility I am thinking about too.

Maybe it's time for me to actually go ahead and make a B/700
motherboard replica? That way all this could be integrated on the same
PCB. :)


--
(\_/) Copy the bunny to your mails to help
(O.o) him achieve world domination.
(> <) Come join the dark side.
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Re: CBM-II solderless memory expansion

MiaM
In reply to this post by Gerrit Heitsch
Den Fri, 13 Apr 2018 21:59:10 +0200 skrev Gerrit Heitsch
<[hidden email]>:

> On 04/13/2018 09:10 PM, Mia Magnusson wrote:
> > Den Fri, 13 Apr 2018 17:46:27 +0200 skrev Michał Pleban
> > <[hidden email]>:
> >> Hello!
> >>
> >> Gerrit Heitsch wrote:
> >>
> >>> A 4464 cannot be put in place of a 4164, so I don't quite see how
> >>> to make that 'solderless'... Could you provide a bit more detail?
> >>
> >> The high-profile board has 128 kB soldeded and sockets for
> >> additional 128 kB RAM. The board with 4464's would go into these
> >> sockets.
> >
> > You might aswell go for 41256 or 44256 then.
>
> 44256 need more refresh... 41256 and 4464 use 8 Bit refresh, just
> like most 4164, but the 44256 need a 9 Bit refresh which you will
> have to generate in some way or you will lose data.
 
Oh, thanks, I've totally missed that.

The signal that controls the existing refresh counters seems to be
available in the expansion connector as RDY which would need to be
combined with P2REFGNT in the coprocessor socket. Those two combined
could control a counter for the extra bits a 44256 (or higher) needs.


--
(\_/) Copy the bunny to your mails to help
(O.o) him achieve world domination.
(> <) Come join the dark side.
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Re: CBM-II solderless memory expansion

Michał Pleban
In reply to this post by MiaM
Hello!

Mia Magnusson wrote:

> You could place those on a pcb in the PLA socket.

No, because these signals do not go to the PLA.

Regards,
Michau.

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Re: CBM-II solderless memory expansion

Jim Brain
In reply to this post by MiaM
What about making a small board that fits in the sockets and switches
the RAM to SRAM?  I've done that for the TANDY Color Computer, so I have
a working circuit.
Jim

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Re: CBM-II solderless memory expansion

David Wood-2
Pseudo DRAM ;)

On Fri, Apr 13, 2018 at 5:54 PM, Jim Brain <[hidden email]> wrote:
What about making a small board that fits in the sockets and switches the RAM to SRAM?  I've done that for the TANDY Color Computer, so I have a working circuit.
Jim


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Re: CBM-II solderless memory expansion

Michał Pleban
In reply to this post by Jim Brain
Hello!

Jim Brain wrote:

> What about making a small board that fits in the sockets and switches
> the RAM to SRAM?  I've done that for the TANDY Color Computer, so I have
> a working circuit.

Do you have a schematic for it?

Regards,
Michau.


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Re: CBM-II solderless memory expansion

Mike Naberezny
In reply to this post by Michał Pleban
On 4/12/18 1:05 PM, Michał Pleban wrote:
> The widely known method of expanding a CBM-II memory requires soldering
> several things on the motherboard, which is doable but not for the faint
> of the heart.
>
> Alternatively you can also use the expansion port to connect a big SRAM
> chip which could expand the memory for the 6509, but it would not be
> seen by the 8088 card.

In the mid-1980's, a member of the Chicago B128 Users Group (CBUG) produced a
plug-in board called B1024.  It provides 1 megabyte using 41256 DRAMs.

I have a B1024 board put some information about it here:
http://mikenaberezny.com/hardware/cbm-ii/b1024-ram-expansion-board/

Regards,
Mike

--
Mike Naberezny ([hidden email]) http://6502.org


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Re: CBM-II solderless memory expansion

Michał Pleban
Hello!

Mike Naberezny wrote:

> In the mid-1980's, a member of the Chicago B128 Users Group (CBUG)
> produced a plug-in board called B1024.  It provides 1 megabyte using
> 41256 DRAMs.
>
> I have a B1024 board put some information about it here:
> http://mikenaberezny.com/hardware/cbm-ii/b1024-ram-expansion-board/

That looks intresting! But judging from the photo and the components on
the board, it reproduces Mia's idea of hooking both to the 6509
expansion port aand 8088 memory port in order to replicate the
multiplexers on the mainboard. A good side is that it doesn't require
replacing the PLA or sticking anything into the RAM sockets on the
mainboard. A downside is that it requires lots of additional compoments
to replicate those already on the mainboard.

Regards,
Michau.

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Re: CBM-II solderless memory expansion

MiaM
In reply to this post by Michał Pleban
Den Fri, 13 Apr 2018 23:02:07 +0200 skrev Michał Pleban
<[hidden email]>:
> Hello!
>
> Mia Magnusson wrote:
>
> > You could place those on a pcb in the PLA socket.
>
> No, because these signals do not go to the PLA.

The existing A0-A15 go to the existing MUXes on the motherboard

P0-P3 (at that point called BP0-BP3) goes to the PLA. Those would need
to be multiplexed (or in general processed) by a PLA replacement.

--
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(O.o) him achieve world domination.
(> <) Come join the dark side.
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Re: CBM-II solderless memory expansion

Mike Naberezny
In reply to this post by Michał Pleban
On 4/13/18 5:21 PM, Michał Pleban wrote:
> That looks intresting! But judging from the photo and the components on
> the board, it reproduces Mia's idea of hooking both to the 6509
> expansion port aand 8088 memory port in order to replicate the
> multiplexers on the mainboard. A good side is that it doesn't require
> replacing the PLA or sticking anything into the RAM sockets on the
> mainboard. A downside is that it requires lots of additional compoments
> to replicate those already on the mainboard.

Even with the extra chips, the B1024 board fits in the low profile case.

If the goal is to have a solderless expansion, this may be a good approach
because the RAM on the mainboard is not always socketed.  I know this from
first-hand experience.  My own machine did not have sockets originally.  You
can see a photo of it here:

http://mikenaberezny.com/hardware/cbm-ii/b128-256k-upgrade/

There is no surviving schematic or documentation for the B1024 board but
advertisements said it could simply be plugged in.  There was no mention of
needing to remove the RAM from the mainboard.  I tried it briefly with the RAM
still on the mainboard and the machine seemed to work fine.  I then installed
sockets and now I don't have any RAM on the mainboard.

Regards,
Mike

--
Mike Naberezny ([hidden email]) http://6502.org


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RE: CBM-II solderless memory expansion

Baltissen, GJPAA (Ruud)
In reply to this post by Michał Pleban
Hallo Michał,


> Do you possibly have a 82S100 symbol for Eagle?

Sorry for answering only now. I have the one used in the C64. Will send it to you this evening.


Met vriendelijke groet / With kind regards, Ruud Baltissen

www.Baltissen.org






De informatie in dit e-mailbericht is vertrouwelijk en uitsluitend bestemd voor de
geadresseerde. Wanneer u dit bericht per abuis ontvangt, verzoeken wij u contact op te
nemen met de afzender per kerende e-mail. Verder verzoeken wij u in dat geval dit
e-mailbericht te vernietigen en de inhoud ervan aan niemand openbaar te maken.
Wij aanvaarden geen aansprakelijkheid voor onjuiste, onvolledige dan wel ontijdige
overbrenging van de inhoud van een verzonden e-mailbericht, noch voor daarbij
overgebrachte virussen.

APG Groep N.V. is gevestigd te Heerlen en is ingeschreven in het
handelsregister van de Kamer van Koophandel Limburg onder nummer 14099617


The information contained in this e-mail is confidential and may be privileged.
It may be read, copied and used only by the intended recipient.
If you have received it in error, please contact the sender immediately by
return e-mail; please delete in this case the e-mail and do not disclose its
contents to any person. We don't accept liability for any errors, omissions,
delays of receipt or viruses in the contents of this message which arise as a
result of e-mail transmission.

APG Groep N.V. is registered in the trade register of the Chamber
of Commerce Limburg, The Netherlands, registration number: 14099617
12