!RSEL signal at s1985 chip (msx2 engine)

Prophet (3031)

03-01-2007, 23:30

A friend and me are wondered about that signal...... we already readed the s1985 pdf and it is not very clear....

so we ran to see the msx2 schematics of our loved msx2....

and we are very confused.... what does!... how to use....

At the talent tpc310

a NAND with multiple inputs is inputed A8 up to A13 in the way that !RSEL is ACTIVE (low) when the Z80 acceses to &Hxx111111xxxxxxxx in short term (the last 256bytes of any page)

So we are so confused and wondered that we want to know.... please geeks.!

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Por NYYRIKKI

Enlighted (6036)

04-01-2007, 07:36

AFAIK it is somehow used to select sub-slot, so this is part of that POKE -1,xxx thing. I'm guessing that maybe these A14,A15 and 8 lower bits are checked by the s1985 by it self (?)

BTW congrats for the 1111:th message

Por POISONIC

Paladin (1012)

04-01-2007, 07:52

and you with the 990th post

Por ro

Scribe (4924)

04-01-2007, 08:12

AFAIK it is somehow used to select sub-slot, so this is part of that POKE -1,xxx thing. I'm guessing that maybe these A14,A15 and 8 lower bits are checked by the s1985 by it self (?)

BTW congrats for the 1111:th message
hehe, yeah only 15 posts (bin).. pff, tosser!

Por flyguille

Prophet (3031)

04-01-2007, 18:58

yeah that was....

the s1985 chip has pin inputs for A15 A14 and A7 up to A0 but hasn't inputs for A13~A8 and no more pins left.... so they uses ONE pin to check if all A13~A8 are at 1. SO in that way the s1985 chip can know when is accesed to &HFFFF memory.

Now, that is perfectly understable.....

The manual says that can be subexpanded slot 0 and slot 3 at the same time... that capability is what I am wondering about.... because that means that there is two registers for &Hffff one for slot 0 and other for slot 3 (as the standard says).... how to use this?.... how complicated is to mod?