2nd OpCode question.... pretty please...

Comments

• ccowley

  February 2012 edited February 2012

  Korinel wrote: »

  Whats 0xED 0x70 please?
  
  Sean's doc says: IN F,(C)* / IN (C)*
  
  That doesn't mean much to me :(
  Lower down in Sean's doc it says: ED 70 is IN F,(n) so would that would make it make it the same as IN A,(n) but with the flag register?
  
  Is (C) = BC?

  Yes (C) = BC. The port identified by BC is read, and the Flag register is set accordingly (so the Zero flag is set if the value read is zero, and Sign, 3, and 5 are copied from the value read, etc), but the actual value read is discarded. So it's the same as, say, IN A,(c) except the A register isn't affected.
  
  As least, that's what vbSpec does. And nobody ever complained.
• Korinel

  February 2012 edited February 2012

  ccowley wrote: »

  Yes (C) = BC. The port identified by BC is read, and the Flag register is set accordingly (so the Zero flag is set if the value read is zero, and Sign, 3, and 5 are copied from the value read, etc), but the actual value read is discarded. So it's the same as, say, IN A,(c) except the A register isn't affected.
  
  As least, that's what vbSpec does. And nobody ever complained.

  
  Ah yes that makes perfect sense :) Thank-you!