Routines
Prev: 82D4 Up: Map Next: 8375
8341: Get an edge change from tape
Used by the routine at 8000.
Input
IX Current address to load the next byte
B On entry, time to find an edge change. On exit, holds the time taken to find it.
C Holds the amount to decrease in the hash byte for each animation data set (usually 1 or 2, but can be more if lots of animation queued)
F On exit, the carry flag is set on success, or reset on failure
8341 EXX Store registers
8342 LD DE,$806B Point DE to the animation queue
8345 LD HL,$8029 Point HL to the animation data
8348 LD B,$05 Initialise timing constant
834A CALL $8351 Read an edge into the alternate registers
834D RET NC Bail out if error
834E EXX Restore registers
834F LD B,$06 Number of bytes for each character
8351 LD A,(HL) Reduce current hash value
8352 SUB C
8353 LD (HL),A
8354 LD A,L Did the hash value overflow?
8355 JR C,$835A Move on if it did
8357 NOP
8358 JR $835C Move on to next value
835A LD (DE),A Set next animation character to queue
835B INC E Move onto the next
835C ADD A,$06 Point to the next sprite data
835E LD L,A
835F DJNZ $8351
8361 EXX Restore registers
Sample a bit from the EAR port. This routine is similar to the LD_SAMPLE routine at 05ED in the ROM. This entry point is used by the routine at 82D4.
8362 AND A Test edges are still found or pending
8363 INC B Increase number of attemps to find edges
8364 RET Z Return if it's taken too long
8365 LD A,$7F Get the EAR bit and SPACE - B section of the keyboard
8367 IN A,($FE)
8369 RRA
836A RET NC Bail out if BREAK was pressed
836B XOR C Test the EAR bit against the expected edge state
836C AND $20
836E JR Z,$8363 Loop back if it has not changed
8370 LD A,C Set last edge type
8371 CPL
8372 LD C,A
8373 SCF Signal okay
8374 RET
Prev: 82D4 Up: Map Next: 8375