Posted By
icbrkr
on 2015-08-07
14:22:11
|  Making a cartridge...
I popped open a C16 tutor cart and was happy to see that it had a ROM chip, socketed, as well as an extra socket that was empty.
I was going to replace the ROM in there with an EPROM but had a couple of quick questions..
I'm assuming that the cartridge layout is banked.. would it be a good guess that it's 8K per socket?
And lastly, what memory location and byte-combo does the Plus/4 check to see if there is an executable cartridge in the slot?
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Posted By
JamesC
on 2015-08-08
02:13:55
| Re: Making a cartridge...
16K. The slot that held the ROM maps in at $8000, the other slot maps in at $C000.
Cartridge ROM must follow this sequence to be recognized:
$8000-8002 4C xx xx (where xx xx is the cold start address within your ROM)
$8003-8005 4C xx xx (duplicate the previous line; this is intended for warm start but hardly anyone uses it)
$8006 Unique cartridge number (please select a value $10-$FF if you want it to appear on a function key, or 01 = autostart)
$8007-800a the ASCII characters 'C B M'
You can look at any CRT on Plus/4 World with a hex editor to see how other programmers do it, but basically if you follow this setup the Plus/4 or C16 will know what to do with your cartridge. 
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Posted By
siz
on 2015-08-08
01:41:29
| Re: Making a cartridge...
Minor correction: the built-in mapping (chip select signals) for cartridge ROMs are really 16k and the lo-one maps to $8000 but the hi-one maps to $c000 (not $a000).
In that particular cartridge you have to check the type of the existing ROM. It's possible that it's a 8k one and the cartridge can handle 16k in total with 2 8k ROMs. But it seems more logical that it has two 16k banks as JamesC suggested.
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Posted By
JamesC
on 2015-08-08
02:16:11
| Re: Making a cartridge...
@Siz, I have corrected my post. Thank you for pointing out my typo.
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Posted By
icbrkr
on 2015-08-08
10:07:15
| Re: Making a cartridge...
Awesome, that's what I was looking for.
Interestingly enough, that's pretty much exactly what a C64 does when looking for a cart (even down to the same memory map for the LO ROM)
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