Inquiry about a custom Amiga project #1
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Hi, I'm not quite sure I follow what you are after. You want a board with one plug (that installs to the motherboard) and two PLCC-84 sockets on top, one socket for OCS Agnus and one for ECS Agnus? and then be able to switch between them (be it offline). OCS Agnus (8371 or earlier) can only address up to 512 kB of Chip RAM and the ECS Agnus supersedes it so I must be missing something why you simply just don't replace the OCS version? If your ECS Agnus has the other pinout there are already adapter boards out there for this purpose where you can retrofit for example a ECS Agnus 390544-01 that normally sits in an A500+/A600 but can be fitted into a machine that take the other pinout (A500, A2000, A3000). This page is a good source just to clarify OCS vs. ECS when we talk about Agnus, the Chips by capability section... |
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Hi,
My request might sound weird, but the idea is to keep the original hardware
my Amiga came from (OCS Agnus) for max compatibility and a bit of simply
keeping original hardware inside with a switch to ECS1MB Agnus, without
fiddling with 40 year old plastics once I plop the switchboard in.
I know I can just plop in ECS 1MB Agnus, or get a board for 2MB Agnus, but
as I said, I'm looking for a mix of original hardware with an on demand
upgrade.
Did I make more sense?
…On Fri, Dec 6, 2024, 12:11 Jorgen Bilander ***@***.***> wrote:
Hi, I'm not quite sure I follow what you are after. You want a board with
one plug (that installs to the motherboard) and two PLCC-84 sockets on top,
one socket for OCS Agnus and one for ECS Agnus? and then be able to switch
between them (be it offline).
OCS Agnus (8371 or earlier) can only address up to 512 kB of Chip RAM and
the ECS Agnus supersedes it so I must be missing something why you simply
just don't replace the OCS version? If your ECS Agnus has the other pinout
there are already adapter boards out there for this purpose where you can
retrofit for example a ECS Agnus 390544-01 that normally sits in an
A500+/A600 but can be fitted into a machine that take the other pinout
(A500, A2000, A3000).
This page is a good source just to clarify OCS vs. ECS when we talk about
Agnus, the *Chips by capability* section...
https://en.wikipedia.org/wiki/MOS_Technology_Agnus
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Hi, ok I see. Yeah that is a bit of an odd request. The ECS Agnus can do all that your OCS Agnus can do plus more so you won't lose any compatibility, but rather you increase it since ECS Agnus can also switch between PAL and NTSC mode. There's no reason for having the OCS Agnus around once you have the ECS Agnus installed. Just tape it somewhere inside the case if you don't wanna lose it and keep it with the machine it came. A very common modification that people do with for example a Rev 5 A500 is to replace the OCS 8370/8371 with a ECS 8372A in order to be able to have a system with 1 MB of Chip RAM. Pin 41 on 8372A controls startup mode PAL or NTSC. What people often do in order to have the system startup in PAL mode is to put a small piece of kapton tape on the chip pin 41 to isolate the pin from touching the corresponding socket pin (which is normally grounded on the motherboard), if that pin is grounded it means startup in NTSC-mode. |
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Pretty much boils to what you said - just tape it somewhere.
Which give me an idea - why not still have it plugged in, somehow.
There are so many physical switchers and boards, so why not Agnus, seemed
like just a few sockets and a bunch of traces (dunno about the switcher
tho) kind of project.
…On Sun, Dec 8, 2024, 11:38 Jorgen Bilander ***@***.***> wrote:
Hi, ok I see.
Yeah that is a bit of an odd request. The ECS Agnus can do all that your
OCS Agnus can do plus more so you won't lose any compatibility, but rather
you increase it since ECS Agnus can also switch between PAL and NTSC mode.
There's no reason for having the OCS Agnus around once you have the ECS
Agnus installed. Just tape it somewhere inside the case if you don't wanna
lose it and keep it with the machine it came.
A very common modification that people do with for example a Rev 5 A500 is
to replace the OCS 8370/8371 with a ECS 8372A in order to be able to have a
system with 1 MB of Chip RAM. Pin 41 on 8372A controls startup mode PAL or
NTSC. What people often do in order to have the system startup in PAL mode
is to put a small piece of kapton tape on the chip pin 41 to isolate the
pin from touching the corresponding socket pin (which is normally grounded
on the motherboard), if that pin is grounded it means startup in NTSC-mode.
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Hello,
I saw your Amiga oriented GitHub repositories, and saw your PLCC-84-plug.
I'm asking if you'd be willing to consider making a dual Agnus 2xPLCC socket board with a switcher.
As I like to do as little fiddling as possible with old hardware, having an Agnus switcher (between OCS and ECS, specifically 1MB only) would mean a tremendous lot for me, as I'd plug that in once, forget about it and reduce any further strenuous activity on that Agnus socket and Agnus itself.
There is even a PLCC84 plug from 2 different sources for fitting this custom board into the Agnus socket, and since I want only the 1MB 8372(A) ECS Agnus (there are 2 specific 8375 1MB that are pin compatible too) there is no need for any converters.
If you're interested, I can make a little donation, or buy it straight from you preassembled, the BOM will possibly be really small AFAIK, I can source my own Agnuses.
You could further experiment with this approach to switch between OCS and ECS 2MB versions, but I just need the OCS and ECS 1MB approach.
Please let me know if you plan on doing this!
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