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View topic - SMS 32K Cart (with bugs?)

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  • Joined: 01 Sep 2018
  • Posts: 10
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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: 123
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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
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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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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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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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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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