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Elite on the BBC Micro

Utility routines: backtonormal (6502SP version)

Name: backtonormal [View in context] Type: Subroutine Category: Utility routines Summary: Disable the keyboard, set the SVN flag to 0, and return with A = 0
.backtonormal LDA #VIAE \ Send a #VIAE %00000001 command to the I/O processor to JSR OSWRCH \ set 6522 System VIA interrupt enable register IER LDA #%00000001 \ (SHEILA &4E) bit 1 (i.e. disable the CA2 interrupt, JSR OSWRCH \ which comes from the keyboard) LDA #0 \ Set the SVN flag to 0 and return from the subroutine BEQ DODOSVN \ using a tail call (this BEQ is effectively a JMP as A \ is always zero)