- Joined: 01 Jul 2016
- Posts: 55
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Basic 32K cart
Posted: Mon Feb 13, 2017 12:31 pm Last edited by KanedaFr on Wed Feb 15, 2017 9:43 am; edited 1 time in total
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Hi,
Since I, at last, finished fixing my game, I'd like to make a physical version of it ;)
So I browsed littlescale blog and Maxim's pinouts page, plus some others related related posts.
While I was pretty confident at first, I started to get some trouble when I discovered the bus was shared with RAM (?)
I'd like to be sure I didn't miss a thing
Let's say I want to use 28C256
ROM <= CARTSLOT
- A0-14 <= A0-14
- D0-7 <= D0-7
- +5V <= +5V
- GND <= GND
- !CE <= !CE or (!CE OR !M0-7) ?
- !OE <= !Rd or !M0-7 or (!Rd OR !M0-7) ?
- !WE <= +5V
As you can see, I'm not sure of !CE and !OE
I saw a lot of home made card used the basic way (!CE / !M0-7) but is it really safe ?
I had the feeling it's safe on this basic 32K ROM only cart but it won't if I add a mapper and, even worst, a RAM onboard...
Bonus question, if I want to use a 29F256 flash without remove it from the cart, with a SMS slot to eeprom-burner adapter
I'll need to use the !WE and so is it correct to use
!WE <= (!Wr OR !M0-7)
to avoid problem while writing to System RAM ?
Thanks
EDIT: fixed an very awful error, using AND while we need OR
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- Joined: 14 Aug 2000
- Posts: 740
- Location: Adelaide, Australia
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Posted: Tue Feb 14, 2017 2:11 am
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Yes you can use !CE / !M0-7.
The easiest way to do this is to get a 32kB cart like Super Tennis, remove the PROM and insert your EPROM/Flash on to the PCB.
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- Joined: 24 Sep 2013
- Posts: 141
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Posted: Wed Feb 15, 2017 7:46 pm
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Simplest cart I made was using an OR gate with !CE and !M0-7 (Or A15, which is the same signal)
_____
!M0-7 --| |
| >=1 |---- !ROM_CE
!CE ----|_____|
.
I'd recommend a 74LS32 (not HC) since you can leave the unused inputs floating. This design is safe as far as I have tested.
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- Joined: 31 Oct 2007
- Posts: 853
- Location: Estonia, Rapla city
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Posted: Wed Feb 15, 2017 9:43 pm
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Floating inputs are a bad design practice regardless of logic family.
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