Spectrum ROM | Routines |
Prev: 03739 | Up: Map |
The address of this routine is found in the parameter table.
The one hundred and seventy six pixel lines of the display are dealt with one by one.
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COPY | 03756 | DI | The maskable interrupt is disabled during COPY. | ||||
03757 | LD B,176 | The 176 lines. | |||||
03759 | LD HL,16384 | The base address of the display. | |||||
The following loop is now entered.
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COPY_1 | 03762 | PUSH HL | Save the base address and the number of the line. | ||||
03763 | PUSH BC | ||||||
03764 | CALL COPY_LINE | It is called 176 times. | |||||
03767 | POP BC | Fetch the line number and the base address. | |||||
03768 | POP HL | ||||||
03769 | INC H | The base address is updated by 256 locations for each line of pixels. | |||||
03770 | LD A,H | Jump forward and hence round the loop again directly for the eight pixel lines of a character line. | |||||
03771 | AND 7 | ||||||
03773 | JR NZ,COPY_2 | ||||||
For each new line of characters the base address has to be updated.
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03775 | LD A,L | Fetch the low byte. | |||||
03776 | ADD A,32 | Update it by +20 bytes. | |||||
03778 | LD L,A | The carry flag will be reset when 'within thirds' of the display. | |||||
03779 | CCF | Change the carry flag. | |||||
03780 | SBC A,A | The A register will hold +F8 when within a 'third' but +00 when a new 'third' is reached. | |||||
03781 | AND 248 | ||||||
03783 | ADD A,H | The high byte of the address is now updated. | |||||
03784 | LD H,A | ||||||
COPY_2 | 03785 | DJNZ COPY_1 | Jump back until 176 lines have been printed. | ||||
03787 | JR COPY_END | Jump forward to the end routine. |
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