Mapping of Memory

[alex3331]

After considering at how 74LS283 works, I do see that SW3 with 128 K EEPROM is not effectively used. Right now there are two 64 kB banks, each of them can be addressed at 0000, 4000, 8000 or C000. This is only 8 combinations of A14, A15 and MA14, MA15, MA16 switches out of available 16.
It is possible to use 256 k or 512 k EEPROM. By the way - it is a lot easier and cheaper to buy SST 39SF040 (512 k) - other IC's (010 and 020) are backordered indefinitely. Let me know what you think. 8 and 32K games work fine, I am experimenting with larger games.
Let me know if I am wrong. Thanks

[apoloval]

Yes, totally right. We are using only 3-bits to indicate the 16KB offset in the ROM. That only covers a ROM address space of 128KB. By adding another bit we could handle 256KBs.

However, let me insist that the 128KB design is incomplete. It was never tested in production. And not intended for use.

[alex3331]

Hello, I finally made this design work. I can put four programs up to 32 k each into a 128 k ROM. All I had to do is to change polarity around DIP switches. Everything works fine. I added 2 more DIP switches and now can use 512 k ROM to store and run 16 games. I need to update PCB but I do not have all of your libraries. I can share an updated schematics if you are interested.

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Sent from my iPad

On Apr 21, 2022, at 4:19 AM, Alvaro Polo ***@***.***> wrote: Yes, totally right. We are using only 3-bits to indicate the 16KB offset in the ROM. That only covers a ROM address space of 128KB. By adding another bit we could handle 256KBs. However, let me insist that the 128KB design is incomplete. It was never tested in production. And not intended for use. — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you authored the thread.

[alex3331]

If you are interested - this works.

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On Thu, Apr 21, 2022 at 6:15 AM Vinci18 ***@***.***> wrote: Hello, I finally made this design work. I can put four programs up to 32 k each into a 128 k ROM. All I had to do is to change polarity around DIP switches. Everything works fine. I added 2 more DIP switches and now can use 512 k ROM to store and run 16 games. I need to update PCB but I do not have all of your libraries. I can share an updated schematics if you are interested. Sent from my iPad On Apr 21, 2022, at 4:19 AM, Alvaro Polo ***@***.***> wrote: Yes, totally right. We are using only 3-bits to indicate the 16KB offset in the ROM. That only covers a ROM address space of 128KB. By adding another bit we could handle 256KBs. However, let me insist that the 128KB design is incomplete. It was never tested in production. And not intended for use. — Reply to this email directly, view it on GitHub <#3 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AIJTZWI3FDVMXMG7JP22XXDVGEFRXANCNFSM5PE7EZXA> . You are receiving this because you authored the thread.Message ID: ***@***.***>

-- Alex Shakhnovich

[apoloval]

What do you mean by change polarity around DIP switches?

[retrolab-ad]

Hello.
Is there any 128k schematic working to share?
Thanks

[apoloval]

Is there any 128k schematic working to share?

Sorry, not yet.

[retrolab-ad]

Gracias El ds., 15 d’oct. 2022, 12:27, Alvaro Polo ***@***.***> va escriure:

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Is there any 128k schematic working to share? Sorry, not yet. — Reply to this email directly, view it on GitHub <#3 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ATJ3I3L67UZZ5HLWIMSU7XDWDKBJFANCNFSM5PE7EZXA> . You are receiving this because you commented.Message ID: ***@***.***>

[elosha]

@alex3331

All I had to do is to change polarity around DIP switches.

Could you please elaborate on that what exactly you mean? Thanks 😃