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Routines |
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Used by the routine at PrintWriteACharacterToTheScreen.
Copies eight pixel rows of the text line at 5020 to the ZX printer through port FB when the printer-on flag at B6F2 is set.
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| ZXPrinter | 8B22 | LD A,($B6F2) | Read the printer-on flag at B6F2. | |
| 8B25 | AND A | Return if the printer is off. | ||
| 8B26 | RET Z | |||
| 8B27 | PUSH HL | Save the text pointer. The printer row count starts at 01. | ||
| 8B28 | PUSH DE | |||
| 8B29 | PUSH BC | |||
| 8B2A | LD D,$01 | |||
| 8B2C | LD HL,$5020 | Point HL at the text line. | ||
| 8B2F | XOR A | Take zero for the first printer byte. | ||
| 8B30 | LD E,A | Clear the marker's low byte. | ||
| ZXPrinter_WriteAByteToThePrinter | 8B31 | OUT ($FB),A | Write a byte to the printer. | |
| ZXPrinter_Loop | 8B33 | IN A,($FB) | Read the printer port FB. | |
| 8B35 | ADD A,A | Double the printer status. | ||
| 8B36 | JP M,ZXPrinter_RestoreAndReturn | Jump to ZXPrinter_RestoreAndReturn if bit 6 of the printer port is set (no printer attached). | ||
| 8B39 | JR NC,ZXPrinter_Loop | Jump back to ZXPrinter_Loop while bit 7 of the printer port is clear. | ||
| 8B3B | PUSH HL | Save the line address and the marker, and take the row count into A. | ||
| 8B3C | PUSH DE | |||
| 8B3D | LD A,D | |||
| 8B3E | CP $02 | Compare the printer row count with 02. | ||
| 8B40 | SBC A,A | Make A FF when that row count was below 02, and zero otherwise. | ||
| 8B41 | AND E | Build the marker bit from E. | ||
| 8B42 | RLCA | |||
| 8B43 | AND E | |||
| 8B44 | LD D,A | |||
| ZXPrinter_ReadAByteFromThePointer | 8B45 | LD C,(HL) | Read a byte from the pointer into C. | |
| 8B46 | PUSH HL | Count 08 passes. | ||
| 8B47 | LD B,$08 | |||
| ZXPrinter_TakeThePrinterByte | 8B49 | LD A,D | Take the byte being sent to the printer. | |
| 8B4A | RLC C | Rotate the next source bit into carry. | ||
| 8B4C | RRA | Shift that bit into the byte for the printer. | ||
| 8B4D | LD H,A | Remember the byte built so far. | ||
| ZXPrinter_WaitWhileThePrinterIsBusy | 8B4E | IN A,($FB) | Read the printer port FB. | |
| 8B50 | RRA | Jump back to ZXPrinter_WaitWhileThePrinterIsBusy while the printer is busy. | ||
| 8B51 | JR NC,ZXPrinter_WaitWhileThePrinterIsBusy | |||
| 8B53 | LD A,H | Take the byte built for the printer. | ||
| 8B54 | OUT ($FB),A | Write a byte to the printer. | ||
| 8B56 | DJNZ ZXPrinter_TakeThePrinterByte | Loop back to ZXPrinter_TakeThePrinterByte until 08 runs out. | ||
| 8B58 | POP HL | Step along the text line at 5020 and continue while a character remains. | ||
| 8B59 | INC HL | |||
| 8B5A | LD A,L | |||
| 8B5B | AND $1F | |||
| 8B5D | JR NZ,ZXPrinter_ReadAByteFromThePointer | |||
| ZXPrinter_WaitUntilThePrinterIsReady | 8B5F | IN A,($FB) | Read the printer port FB. | |
| 8B61 | RRA | Wait until the printer is ready (bit 0 of port FB). | ||
| 8B62 | JR NC,ZXPrinter_WaitUntilThePrinterIsReady | |||
| 8B64 | LD A,D | Take the byte being sent to the printer. | ||
| 8B65 | RRCA | Rotate the next bit out towards the printer. | ||
| 8B66 | OUT ($FB),A | Write a byte to the printer. | ||
| 8B68 | POP DE | Restore DE and HL from the stack, step to the next row, and jump back to ZXPrinter_WriteAByteToThePrinter if bit 3 of E is clear. | ||
| 8B69 | POP HL | |||
| 8B6A | INC H | |||
| 8B6B | INC E | |||
| 8B6C | BIT 3,E | |||
| 8B6E | JR Z,ZXPrinter_WriteAByteToThePrinter | |||
| 8B70 | LD A,$04 | Send 04 to the printer port. | ||
| 8B72 | OUT ($FB),A | Write a byte to the printer. | ||
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Restore the registers saved for the printer.
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| ZXPrinter_RestoreAndReturn | 8B74 | POP BC | Restore BC, DE and HL from the stack. | |
| 8B75 | POP DE | |||
| 8B76 | POP HL | |||
| 8B77 | RET | Return. | ||
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