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| 2 | | glcplot.s -- plot a pixel on the LCD display
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| 3 | | Version 2 -- 1987-04-23 -- D.N. Lynx Crowe
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| 4 | | (c) Copyright 1987 -- D.N. Lynx Crowe
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| 5 |
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| 6 | | GLCplot(x, y, val)
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| 7 | | unsigned x, y, val);
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| 8 |
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| 9 | | Plot a pixel at ('x', 'y') using lcdbase as the plane address
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| 10 | | in GLC RAM. If 'val' is zero, the pixel is cleared,
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| 11 | | otherwise the pixel is cleared. No error checking is done.
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| 12 | | Limits: 0 LE x LE 511, 0 LE y LE 63.
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| 13 | | ------------------------------------------------------------------------------
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| 14 | .text
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| 15 |
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| 16 | .xdef GLCplot
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| 17 | .xref lcd_a0,lcd_a1,lcdbase
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| 18 |
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| 19 | XLOC = 8 | 'x' parameter offset
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| 20 | YLOC = 10 | 'y' parameter offset
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| 21 | VAL = 12 | 'val' parameter offset
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| 22 |
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| 23 | G_CRSWR = 0x46 | GLC set cursor command
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| 24 | G_MWRITE = 0x42 | GLC write command
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| 25 | G_MREAD = 0x43 | GLC read command
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| 26 |
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| 27 | .page
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| 28 |
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| 29 | GLCplot: link a6,#0 | Link stack frames
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| 30 | moveq #63,d0 | d0 = (63-y) * 85
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| 31 | sub.w YLOC(a6),d0 | ...
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| 32 | mulu #85,d0 | ...
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| 33 | clr.l d1 | d1 = x/6
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| 34 | move.w XLOC(a6),d1 | ...
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| 35 | divu #6,d1 | ...
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| 36 | add.w d1,d0 | d0 = (63-y)*85 + (x/6)
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| 37 | swap d1 | d2 = 7 - (x%6) % 8
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| 38 | moveq #7,d2 | ...
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| 39 | sub.w d1,d2 | ...
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| 40 | andi.w #7,d2 | ...
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| 41 | lsr.w #3,d1 | d1 = (x%6) / 8
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| 42 | add.w d1,d0 | d0 = cursor address
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| 43 | add.w lcdbase,d0 | ...
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| 44 | move.w d0,d1 | d1 = cursor address, too
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| 45 | move.b #G_CRSWR,lcd_a1 | Send cursor address to GLC
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| 46 | move.b d0,lcd_a0 | ...
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| 47 | lsr.w #8,d0 | ...
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| 48 | move.b d0,lcd_a0 | ...
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| 49 | move.b #G_MREAD,lcd_a1 | Read old pixel byte
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| 50 | move.b lcd_a1,d0 | ... into d0
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| 51 | tst.w VAL(a6) | Check val for zero
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| 52 | beq glcplt1 | Jump if val EQ 0
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| 53 |
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| 54 | bset d2,d0 | Set the pixel to 1
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| 55 | bra glcplt2 | Go write pixel to GLC
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| 56 |
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| 57 | glcplt1: bclr d2,d0 | Clear the pixel to 0
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| 58 |
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| 59 | glcplt2: move.b #G_CRSWR,lcd_a1 | Send cursor address to GLC
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| 60 | move.b d1,lcd_a0 | ...
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| 61 | lsr.w #8,d1 | ...
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| 62 | move.b d1,lcd_a0 | ...
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| 63 | move.b #G_MWRITE,lcd_a1 | Setup GLC to write pixel
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| 64 | move.b d0,lcd_a0 | Write pixel
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| 65 | unlk a6 | Unlink stack frames
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| 66 | rts | Return to caller
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| 67 |
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| 68 | .end
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