Routines
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21920: Count down from 9 to 0
Continues from the routine at 33204. Counts down from 9 to 0, giving the user a chance to set the input method and change the characters' names before the game starts.
Input
BC 256
DE 33024
HL 23296
21920 LDIR Copy 256 bytes from 23296 to 33024
21922 LD H,88 INK 1: PAPER 1
21924 LD B,3
21926 LD D,H
21927 INC E
21928 LD (HL),9
21930 LDIR
21932 LD HL,23611 Reset bit 5 at 23611, ready for future keypresses
21935 RES 5,(HL)
21937 EXX Point HL' at the last byte of the graphic data for the digit '9' in the ROM
21938 LD HL,15823
21941 EXX
21942 LD DE,1084 Wait approximately one second
21945 DJNZ 21945
21947 DEC DE
21948 LD A,D
21949 OR E
21950 JR NZ,21945
21952 LD HL,23020 23020 is the attribute file address where the bottom row of 'big pixels' will be drawn
21955 LD DE,65496 DE=-40
21958 LD C,8 There are 8 pixel rows per countdown digit
21960 EXX
21961 BIT 7,L Set the zero flag when HL' hits 15743
21963 LD A,(HL) Pick up a digit pixel row byte
21964 DEC HL Move HL' to the next pixel row up
21965 EXX
21966 JP Z,21737 Start the game if we've already printed '0'
21969 LD B,8 There are 8 bits per pixel row
21971 LD (HL),9 INK 1: PAPER 1 (blue) for a reset pixel
21973 RLCA Is this a reset pixel?
21974 JR NC,21978 Jump if so
21976 LD (HL),36 INK 4: PAPER 4 (green) for a set pixel
21978 INC HL Move HL along to the next attribute file address
21979 DJNZ 21971 Jump back until all 8 'big pixels' have been drawn
21981 ADD HL,DE Move HL back 8 spaces and up one row of the attribute file
21982 DEC C Next pixel row
21983 JR NZ,21960 Jump back until all 8 pixel rows have been drawn
21985 CALL 29012 Make a ticking sound effect
21988 LD HL,23611
21991 BIT 5,(HL) Reset the zero flag if a key was pressed
21993 RES 5,(HL) Reset bit 5 at 23611, ready for future keypresses
21995 JP NZ,21425 Jump if a key was pressed
21998 JR 21942 Wait roughly one second, then print the next digit
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