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  • Joined: 01 Sep 2018
  • Posts: 25
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SMS 32K Cart (with bugs?)
Post Posted: Sat Jun 29, 2019 9:27 pm
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
cart1-sch.png (9.47 KB)
Schematic
cart1-sch.png
cart1-pcb.png (4.88 KB)
PCB
cart1-pcb.png
SMS-cart2.zip (132.37 KB)
Project

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  • Joined: 24 Sep 2013
  • Posts: 138
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Post 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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  • Joined: 01 Sep 2018
  • Posts: 25
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Post 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.
cart1-pcb.png (13.25 KB)
PCB V2
cart1-pcb.png
cart1-sch.png (33.31 KB)
Schematic V2
cart1-sch.png
Cart1-v2.zip (108.34 KB)
Version2

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  • Joined: 14 Aug 2000
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  • Location: Adelaide, Australia
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SMS 32K Cart (with bugs?)
Post Posted: Sun Jun 30, 2019 3:47 pm
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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  • Joined: 08 Sep 2018
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Post 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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  • Joined: 14 Aug 2000
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  • Location: Adelaide, Australia
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SMS 32K Cart (with bugs?)
Post Posted: Mon Jul 01, 2019 5:07 am
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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  • Joined: 01 Sep 2018
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Post 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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  • Joined: 24 Sep 2013
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Post Posted: Mon Jul 01, 2019 5:14 pm
asynchronous wrote
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.


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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  • Joined: 14 Aug 2000
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  • Location: Adelaide, Australia
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SMS 32K Cart (with bugs?)
Post Posted: Tue Jul 02, 2019 4:23 am
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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  • Joined: 08 Jun 2021
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Post Posted: Thu Jul 01, 2021 7:30 pm
NeonMan wrote
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.
[img][/img]
master pcb.png (29.68 KB)
simple project like this already works 32k
master pcb.png

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  • Joined: 27 Jun 2020
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Post 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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  • Joined: 24 Mar 2021
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Post Posted: Fri Jul 02, 2021 4:31 pm
L10N37 wrote
I think he wants a cartridge, not a card
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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