Skip to navigation

Save and load: GTDRV

[6502 Second Processor version]

Name: GTDRV [Show more] Type: Subroutine Category: Save and load Summary: Get an ASCII disc drive number from the keyboard
Context: See this subroutine in context in the source code References: This subroutine is called as follows: * CATS calls GTDRV * QUS1 calls GTDRV

Returns: A The ASCII value of the entered drive number ("0" to "3") C flag Clear if a valid drive number was entered (0-3), set otherwise
.GTDRV LDA #2 \ Print extended token 2 ("{cr}WHICH DRIVE?") JSR DETOK JSR t \ Scan the keyboard until a key is pressed, returning \ the ASCII code in A and X ORA #%00010000 \ Set bit 4 of A, perhaps to avoid printing any control \ characters in the next instruction JSR CHPR \ Print the character in A PHA \ Store A on the stack so we can retrieve it after the \ call to FEED JSR FEED \ Print a newline PLA \ Restore A from the stack CMP #'0' \ If A < ASCII "0", then it is not a valid drive number, BCC LOR \ so jump to LOR to set the C flag and return from the \ subroutine CMP #'4' \ If A >= ASCII "4", then it is not a valid drive \ number, and this CMP sets the C flag, otherwise it is \ a valid drive number in the range 0-3, so clear it RTS \ Return from the subroutine