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SMS 32K Cart (with bugs?)
Posted: Sat Jun 29, 2019 9:27 pm
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I have cobbled together a SMS export cartridge for a 32K eprom (27256)
It is made in Eagle CAD 6 Lite. Now I am looking for bugs in my design. Can you fine folk help me find them if there are any? Here is the library I used to design the pcb: http://www.smspower.org/forums/17192-SegaMasterSystem32KByteCart#103494 |
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Posted: Sun Jun 30, 2019 9:01 am |
ROM !CE line must depend on SMS's !CE since it is the pin that will control whether the console is using the BIOS, Cart, Card or EXT port.
On a working desig I'm using (!CE || !M0-7) but someone correct me if I'm wrong, just using !CE could be enough. |
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Posted: Sun Jun 30, 2019 1:21 pm |
Here is my version 2 of the cart.
It now contains a OR gate to combine !CE and !M0-7 so both need to be low to activate the eprom. |
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SMS 32K Cart (with bugs?)
Posted: Sun Jun 30, 2019 3:47 pm
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Version 2 looks like it should work.
The official 32kB cartridge PCB connects the chip /CE to the slot /CE and the chip /OE to the slot /M0-7. |
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Posted: Sun Jun 30, 2019 4:18 pm |
I dont think the OR gate is necessary to be honest. Ive used designs that do not connect /M0-7 and work perfectly as long as /CE goes to /CE and READ goes to /OE. | |
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SMS 32K Cart (with bugs?)
Posted: Mon Jul 01, 2019 5:07 am
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Using just /CE and /RD won't work. They are not address specific. So you'd be outputting the contents of the Cartridge EPROM for the entire CPU address range; including the range where the DRAM is mapped. | |
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Posted: Mon Jul 01, 2019 11:51 am |
I am now working on a new pcb layout that is not mirrored.
The library that I use has the cardrige-pcb mirrored for some reason. I am going to keep the OR-gate to be on the safe side. The added cost is very low. |
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Posted: Mon Jul 01, 2019 5:14 pm |
Does that mean !M0-7 is essentially (A15 || !MREQ)? I'm interested since it could be useful for some future enhancements on the mapper circuit I've made. Also by extension the remaining !M[range] signals should be (!InRange || !MREQ) I guess. |
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SMS 32K Cart (with bugs?)
Posted: Tue Jul 02, 2019 4:23 am
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Yes that's right.
I have a 48kB cartridge design (somewhere...) that uses a 27C256 and 27C128. You can probably now guess how that design works. :) |
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Posted: Thu Jul 01, 2021 7:30 pm |
[img][/img] |
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Posted: Fri Jul 02, 2021 3:24 am |
I think he wants a cartridge, not a card
that's being done too https://github.com/reidrac/sms-cart-32k I've opened this in kicad and some of the traces are doing weird loops and stuff, he's used autopilot on a few of the traces which is never a good idea. |
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Posted: Fri Jul 02, 2021 4:31 pm |
The formal "Sega Card" has the same "two rows of contacts" that the Game Gear does. Just 35 pins instead of 45. |
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