Difference between revisions of "Z80 port map"

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|NMI disable
 
|NMI disable
 
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Bank selection is made by '''reading''' ports.
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SNK used an obscure feature of the Z80: when accessing ports, the entire address bus is set, not only the lower 8 bits.
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The banks can then be chosen by putting the bank number in B, the port number in C and doing IN A,(C).
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Or by putting the bank number in A and doing IN A,(Port). (to verify)
  
 
[[Category:Base system]]
 
[[Category:Base system]]

Revision as of 04:02, 28 June 2011

Number Read Write
$00 Read sound code from 68k Clear sound code buffer
$08 NMI enable
$04~$07 YM2610 I/O
$08 Set $F000~$F7FF bank
$09 Set $E000~$EFFF bank
$0A Set $C000~$DFFF bank
$0B Set $8000~$BFFF bank
$0C Reply to 68k
$18 NMI disable

Bank selection is made by reading ports. SNK used an obscure feature of the Z80: when accessing ports, the entire address bus is set, not only the lower 8 bits.

The banks can then be chosen by putting the bank number in B, the port number in C and doing IN A,(C). Or by putting the bank number in A and doing IN A,(Port). (to verify)