INT 15,4F - Keyboard Intercept (BIOS date specific)

AH = 4F

AL = scan code

CF = set to 1 (via STC instruction)

on return

AH = 80h, CF set (PC, PCjr)

= 86h, CF set (XT BIOS 11/8/82, AT BIOS 1/10/84)

AL = CF set, new scan code

= CF clear, original scancode

- available with XT BIOS after 11/8/82, AT BIOS after 1/10/84

- called by ~INT 9~, makes allowance for keyboard translation

- normally returns the scan code in AL, with CF set

- if function returns with CF clear, INT 9 ignores keystroke

- do not rely on this function being called for each INT 9 since

any user INT 9 handler can exit prematurely and circumvent

this function