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Hardware > Cartrage Bus

#89615 - lims3000 - Sun Jun 25, 2006 8:20 pm

Hi,
ich have searched all weekend but couldnt find any good documentation on how the actual bus between GBA and cartrage works.
I know so far that it has 16 adress bits an 8 data/adress bits + the RD, WR, and then two CS lines for ROM and RAM.
But I need a diagramm or something allike that shows me, how the data is transferred. When using the ROM 24 adress lines are used but how does the 16 bit data get written then.
Is there any detail on how that bus works?
Pleas help.
Thank you very much in advance ;-)
Regards

#89628 - tepples - Sun Jun 25, 2006 9:24 pm

Think of it as "seek" and "read". As I understand it, the protocol looks like this:
  1. Seek: The GBA puts an address on A23-A16 and AD15-AD0 and sets /CS low. Then the Game Pak ROM copies the contents of A23-A16 and AD15-AD0 to its address counter.
  2. Read: The GBA lets go of AD15-AD0, sets /RD low, waits a few nanoseconds for the Game Pak to put a 16-bit word on AD15-AD0, and finally reads AD15-AD0 while pulling /RD back high. The Game Pak adds 1 to its address counter and waits for another seek or read.

Details of the cart bus are on Reiner Ziegler's page.
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