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Routines |
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Preserve the current registers.
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| ControlCode_BlankScreen | 9903 | PUSH DE | Stash DE and BC on the stack. | |
| 9904 | PUSH BC | |||
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First blank the attribute buffer.
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| 9905 | LD HL,$5800 | HL=5800 (attribute buffer location). | ||
| 9908 | LD DE,$5801 | DE=5801. | ||
| 990B | LD BC,$02FF | BC=02FF. | ||
| 990E | HALT | Halt operation (suspend CPU until the next interrupt). | ||
| 990F | LD (HL),$00 | Write INK: BLACK, PAPER: BLACK to *HL. | ||
| 9911 | LDIR | Copy the 00 to the rest of the attribute buffer. | ||
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Next blank the screen buffer.
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| 9913 | LD B,$C0 | Set a counter in B of C0; which is 24 rows x 8 pixels in each. | ||
| 9915 | LD HL,$4000 | HL=4000 (screen buffer location). | ||
| BlankPixelLine_Loop | 9918 | LD C,L | Save the row start in C. | |
| 9919 | LD A,$20 | Set a counter in A of 20 for the number of bytes in a row. | ||
| BlankByte_Loop | 991B | LD (HL),$00 | Write 00 to *HL. | |
| 991D | INC L | Move to the next byte in this line. | ||
| 991E | DEC A | Decrease the byte counter by one. | ||
| 991F | JR NZ,BlankByte_Loop | Jump back to BlankByte_Loop until the byte clearing is done for this pixel row. | ||
| 9921 | LD L,C | Back to the start of the line. | ||
| 9922 | CALL NextScreenBufferLine | Call NextScreenBufferLine. | ||
| 9925 | DJNZ BlankPixelLine_Loop | Decrease counter by one and loop back to BlankPixelLine_Loop until counter is zero. | ||
| 9927 | JP ControlCode_FullReturn_1 | Jump to ControlCode_FullReturn_1. | ||
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