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00056: THE 'MASKABLE INTERRUPT' ROUTINE
The real time clock is incremented and the keyboard scanned whenever a maskable interrupt occurs.
MASK_INT 00056 PUSH AF Save the current values held in these registers.
00057 PUSH HL
00058 LD HL,(23672) The lower two bytes of the frame counter (FRAMES) are incremented every 20 ms. (U.K.) The highest byte of the frame counter is only incremented when the value of the lower two bytes is zero.
00061 INC HL
00062 LD (23672),HL
00065 LD A,H
00066 OR L
00067 JR NZ,KEY_INT
00069 INC (IY+64)
KEY_INT 00072 PUSH BC Save the current values held in these registers.
00073 PUSH DE
00074 CALL KEYBOARD Now scan the keyboard.
00077 POP DE Restore the values.
00078 POP BC
00079 POP HL
00080 POP AF
00081 EI The maskable interrupt is enabled before returning.
00082 RET
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