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Update apple2_hires.md
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@ -88,4 +88,109 @@ The following code will do it
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So what happens next ?
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So what happens next ? Well, a `POKE 9216,255` will show you that you're plotting on line 1 ! And once line 1 has been filled, you'll plot on line 65 ! And then on line 129 ! Then back to first section of 64-lines but on line 8+1=9, then on line 16+1=17, etc.
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10 HGR
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20 A = 8192: REM $2000
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30 FOR L = 0 TO 7
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40 FOR K = 0 TO 7
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50 FOR J = 0 TO 2
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60 FOR I = 0 TO 39
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70 POKE A, 255
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80 A = A + 1
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90 NEXT I,J
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100 A = A + 8
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110 NEXT K,L
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120 PRINT A
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If you run the above code, your screen will be filled and A will point to 16384 (or $4000) which is the start of page 2.
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To sum it up, the logical structure in RAM is as follows:
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1. There are 3 sections of 64 lines beginning at lines 0, 64 and 128
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2. A Y-line subindex is set to zero
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3. A Y-line index is set to zero
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4. Section number is set to zero
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5. RAM holds the three lines corresponding to the section + index + subindex
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6. Section number is incremented by 64
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7. Back to step 5, three times
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8. Then 8 bytes are wasted
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9. Y-Line index is incremented by 8
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10. Back to step 4, eight times
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11. Y-line SUBindex is incremented by 1
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12. Back to step 3, eight times
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In code that would be
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10 HGR: A = 8192
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20 Y0 = 0 : N0 = 0 : REM Y-SUBINDEX AND COUNTER
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30 Y1 = 0 : N1 = 0 : REM Y-INDEX AND COUNTER
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40 S = 0 : NS = 0 : REM SECTION NUMBER AND COUNTER
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50 HPLOT 0, S + Y0 + Y1 TO 279, S + Y0 + Y1: REM DRAW A WHOLE LINE
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60 PRINT S + Y0 + Y1;": ";A" ";: S = S + 64: A = A + 40
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70 NS = NS + 1 : IF NS < 3 THEN GOTO 50
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80 A = A + 8: REM HERE 8 BYTES ARE NOT USED
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90 Y1 = Y1 + 8
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100 N1 = N1 + 1: IF N1<8 THEN GOTO 40
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110 Y0 = Y0 + 1
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120 N0 = N0 + 1: IF N0<8 THEN GOTO 30: REM WE COULD HAVE USED Y0 ONLY SINCE IT'S ALWAYS EQUAL TO N0
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Notice how the HPLOTs draw the lines in the same order as the `POKE`s in the previous programs.
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The starting address of a line Y in hires page 1 is found using the following formula:
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S = INT(Y/64)
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Y1 = INT( (Y - 64 * S) / 8)
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Y0 = INT(Y - 64 * S - 8 * Y1)
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A = 8192 + S * 40 + Y1 * 128 + Y0 * 1024
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|<sub>Line</sub>|<sub> Start </sub>|<sub> End </sub>|<sub> Line </sub>|<sub> Start </sub>|<sub> End </sub>|<sub> Line </sub>|<sub> Start </sub>|<sub> End </sub>|<sub> Line </sub>|<sub> Start </sub>|<sub> End </sub>|<sub>Line </sub>|<sub> Start </sub>|<sub> End </sub>|<sub> Line </sub>|<sub> Start </sub>|<sub> End </sub>|<sub>Line </sub>|<sub> Start </sub>|<sub> End </sub>|<sub> Line </sub>|<sub> Start </sub>|<sub> End </sub>|
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|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|
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| <sub>**0**</sub> | <sub>$2000</sub> | <sub>$2027</sub> | <sub>**1**</sub> | <sub>$2400</sub> | <sub>$2427</sub> | <sub>**2**</sub> | <sub>$2800</sub> | <sub>$2827</sub> | <sub>**3**</sub> | <sub>$2C00</sub> | <sub>$2C27</sub> | <sub>**4**</sub> | <sub>$3000</sub> | <sub>$3027</sub> | <sub>**5**</sub> | <sub>$3400</sub> | <sub>$3427</sub> | <sub>**6**</sub> | <sub>$3800</sub> | <sub>$3827</sub> | <sub>**7**</sub> | <sub>$3C00</sub> | <sub>$3C27</sub> |
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| <sub>**64**</sub> | <sub>$2028</sub> | <sub>$204F</sub> | <sub>**65**</sub> | <sub>$2428</sub> | <sub>$244F</sub> | <sub>**66**</sub> | <sub>$2828</sub> | <sub>$284F</sub> | <sub>**67**</sub> | <sub>$2C28</sub> | <sub>$2C4F</sub> | <sub>**68**</sub> | <sub>$3028</sub> | <sub>$304F</sub> | <sub>**69**</sub> | <sub>$3428</sub> | <sub>$344F</sub> | <sub>**70**</sub> | <sub>$3828</sub> | <sub>$384F</sub> | <sub>**71**</sub> | <sub>$3C28</sub> | <sub>$3C4F</sub> |
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| <sub>**128**</sub> | <sub>$2050</sub> | <sub>$2077</sub> | <sub>**129**</sub> | <sub>$2450</sub> | <sub>$2477</sub> | <sub>**130**</sub> | <sub>$2850</sub> | <sub>$2877</sub> | <sub>**131**</sub> | <sub>$2C50</sub> | <sub>$2C77</sub> | <sub>**132**</sub> | <sub>$3050</sub> | <sub>$3077</sub> | <sub>**133**</sub> | <sub>$3450</sub> | <sub>$3477</sub> | <sub>**134**</sub> | <sub>$3850</sub> | <sub>$3877</sub> | <sub>**135**</sub> | <sub>$3C50</sub> | <sub>$3C77</sub> |
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| <sub>**wasted**</sub> | <sub>$2078</sub> | <sub>$207F</sub> | <sub>**wasted**</sub> | <sub>$2478</sub> | <sub>$247F</sub> | <sub>**wasted**</sub> | <sub>$2878</sub> | <sub>$287F</sub> | <sub>**wasted**</sub> | <sub>$2C78</sub> | <sub>$2C7F</sub> | <sub>**wasted**</sub> | <sub>$3078</sub> | <sub>$307F</sub> | <sub>**wasted**</sub> | <sub>$3478</sub> | <sub>$347F</sub> | <sub>**wasted**</sub> | <sub>$3878</sub> | <sub>$387F</sub> | <sub>**wasted**</sub> | <sub>$3C78</sub> | <sub>$3C7F</sub> |
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| <sub>**8**</sub> | <sub>$2080</sub> | <sub>$20A7</sub> | <sub>**9**</sub> | <sub>$2480</sub> | <sub>$24A7</sub> | <sub>**10**</sub> | <sub>$2880</sub> | <sub>$28A7</sub> | <sub>**11**</sub> | <sub>$2C80</sub> | <sub>$2CA7</sub> | <sub>**12**</sub> | <sub>$3080</sub> | <sub>$30A7</sub> | <sub>**13**</sub> | <sub>$3480</sub> | <sub>$34A7</sub> | <sub>**14**</sub> | <sub>$3880</sub> | <sub>$38A7</sub> | <sub>**15**</sub> | <sub>$3C80</sub> | <sub>$3CA7</sub> |
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| <sub>**72**</sub> | <sub>$20A8</sub> | <sub>$20CF</sub> | <sub>**73**</sub> | <sub>$24A8</sub> | <sub>$24CF</sub> | <sub>**74**</sub> | <sub>$28A8</sub> | <sub>$28CF</sub> | <sub>**75**</sub> | <sub>$2CA8</sub> | <sub>$2CCF</sub> | <sub>**76**</sub> | <sub>$30A8</sub> | <sub>$30CF</sub> | <sub>**77**</sub> | <sub>$34A8</sub> | <sub>$34CF</sub> | <sub>**78**</sub> | <sub>$38A8</sub> | <sub>$38CF</sub> | <sub>**79**</sub> | <sub>$3CA8</sub> | <sub>$3CCF</sub> |
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| <sub>**136**</sub> | <sub>$20D0</sub> | <sub>$20F7</sub> | <sub>**137**</sub> | <sub>$24D0</sub> | <sub>$24F7</sub> | <sub>**138**</sub> | <sub>$28D0</sub> | <sub>$28F7</sub> | <sub>**139**</sub> | <sub>$2CD0</sub> | <sub>$2CF7</sub> | <sub>**140**</sub> | <sub>$30D0</sub> | <sub>$30F7</sub> | <sub>**141**</sub> | <sub>$34D0</sub> | <sub>$34F7</sub> | <sub>**142**</sub> | <sub>$38D0</sub> | <sub>$38F7</sub> | <sub>**143**</sub> | <sub>$3CD0</sub> | <sub>$3CF7</sub> |
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| <sub>**wasted**</sub> | <sub>$20F8</sub> | <sub>$20FF</sub> | <sub>**wasted**</sub> | <sub>$24F8</sub> | <sub>$24FF</sub> | <sub>**wasted**</sub> | <sub>$28F8</sub> | <sub>$28FF</sub> | <sub>**wasted**</sub> | <sub>$2CF8</sub> | <sub>$2CFF</sub> | <sub>**wasted**</sub> | <sub>$30F8</sub> | <sub>$30FF</sub> | <sub>**wasted**</sub> | <sub>$34F8</sub> | <sub>$34FF</sub> | <sub>**wasted**</sub> | <sub>$38F8</sub> | <sub>$38FF</sub> | <sub>**wasted**</sub> | <sub>$3CF8</sub> | <sub>$3CFF</sub> |
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| <sub>**16**</sub> | <sub>$2100</sub> | <sub>$2127</sub> | <sub>**17**</sub> | <sub>$2500</sub> | <sub>$2527</sub> | <sub>**18**</sub> | <sub>$2900</sub> | <sub>$2927</sub> | <sub>**19**</sub> | <sub>$2D00</sub> | <sub>$2D27</sub> | <sub>**20**</sub> | <sub>$3100</sub> | <sub>$3127</sub> | <sub>**21**</sub> | <sub>$3500</sub> | <sub>$3527</sub> | <sub>**22**</sub> | <sub>$3900</sub> | <sub>$3927</sub> | <sub>**23**</sub> | <sub>$3D00</sub> | <sub>$3D27</sub> |
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| <sub>**80**</sub> | <sub>$2128</sub> | <sub>$214F</sub> | <sub>**81**</sub> | <sub>$2528</sub> | <sub>$254F</sub> | <sub>**82**</sub> | <sub>$2928</sub> | <sub>$294F</sub> | <sub>**83**</sub> | <sub>$2D28</sub> | <sub>$2D4F</sub> | <sub>**84**</sub> | <sub>$3128</sub> | <sub>$314F</sub> | <sub>**85**</sub> | <sub>$3528</sub> | <sub>$354F</sub> | <sub>**86**</sub> | <sub>$3928</sub> | <sub>$394F</sub> | <sub>**87**</sub> | <sub>$3D28</sub> | <sub>$3D4F</sub> |
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| <sub>**144**</sub> | <sub>$2150</sub> | <sub>$2177</sub> | <sub>**145**</sub> | <sub>$2550</sub> | <sub>$2577</sub> | <sub>**146**</sub> | <sub>$2950</sub> | <sub>$2977</sub> | <sub>**147**</sub> | <sub>$2D50</sub> | <sub>$2D77</sub> | <sub>**148**</sub> | <sub>$3150</sub> | <sub>$3177</sub> | <sub>**149**</sub> | <sub>$3550</sub> | <sub>$3577</sub> | <sub>**150**</sub> | <sub>$3950</sub> | <sub>$3977</sub> | <sub>**151**</sub> | <sub>$3D50</sub> | <sub>$3D77</sub> |
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| <sub>**wasted**</sub> | <sub>$2178</sub> | <sub>$217F</sub> | <sub>**wasted**</sub> | <sub>$2578</sub> | <sub>$257F</sub> | <sub>**wasted**</sub> | <sub>$2978</sub> | <sub>$297F</sub> | <sub>**wasted**</sub> | <sub>$2D78</sub> | <sub>$2D7F</sub> | <sub>**wasted**</sub> | <sub>$3178</sub> | <sub>$317F</sub> | <sub>**wasted**</sub> | <sub>$3578</sub> | <sub>$357F</sub> | <sub>**wasted**</sub> | <sub>$3978</sub> | <sub>$397F</sub> | <sub>**wasted**</sub> | <sub>$3D78</sub> | <sub>$3D7F</sub> |
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| <sub>**24**</sub> | <sub>$2180</sub> | <sub>$21A7</sub> | <sub>**25**</sub> | <sub>$2580</sub> | <sub>$25A7</sub> | <sub>**26**</sub> | <sub>$2980</sub> | <sub>$29A7</sub> | <sub>**27**</sub> | <sub>$2D80</sub> | <sub>$2DA7</sub> | <sub>**28**</sub> | <sub>$3180</sub> | <sub>$31A7</sub> | <sub>**29**</sub> | <sub>$3580</sub> | <sub>$35A7</sub> | <sub>**30**</sub> | <sub>$3980</sub> | <sub>$39A7</sub> | <sub>**31**</sub> | <sub>$3D80</sub> | <sub>$3DA7</sub> |
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| <sub>**88**</sub> | <sub>$21A8</sub> | <sub>$21CF</sub> | <sub>**89**</sub> | <sub>$25A8</sub> | <sub>$25CF</sub> | <sub>**90**</sub> | <sub>$29A8</sub> | <sub>$29CF</sub> | <sub>**91**</sub> | <sub>$2DA8</sub> | <sub>$2DCF</sub> | <sub>**92**</sub> | <sub>$31A8</sub> | <sub>$31CF</sub> | <sub>**93**</sub> | <sub>$35A8</sub> | <sub>$35CF</sub> | <sub>**94**</sub> | <sub>$39A8</sub> | <sub>$39CF</sub> | <sub>**95**</sub> | <sub>$3DA8</sub> | <sub>$3DCF</sub> |
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| <sub>**152**</sub> | <sub>$21D0</sub> | <sub>$21F7</sub> | <sub>**153**</sub> | <sub>$25D0</sub> | <sub>$25F7</sub> | <sub>**154**</sub> | <sub>$29D0</sub> | <sub>$29F7</sub> | <sub>**155**</sub> | <sub>$2DD0</sub> | <sub>$2DF7</sub> | <sub>**156**</sub> | <sub>$31D0</sub> | <sub>$31F7</sub> | <sub>**157**</sub> | <sub>$35D0</sub> | <sub>$35F7</sub> | <sub>**158**</sub> | <sub>$39D0</sub> | <sub>$39F7</sub> | <sub>**159**</sub> | <sub>$3DD0</sub> | <sub>$3DF7</sub> |
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| <sub>**wasted**</sub> | <sub>$21F8</sub> | <sub>$21FF</sub> | <sub>**wasted**</sub> | <sub>$25F8</sub> | <sub>$25FF</sub> | <sub>**wasted**</sub> | <sub>$29F8</sub> | <sub>$29FF</sub> | <sub>**wasted**</sub> | <sub>$2DF8</sub> | <sub>$2DFF</sub> | <sub>**wasted**</sub> | <sub>$31F8</sub> | <sub>$31FF</sub> | <sub>**wasted**</sub> | <sub>$35F8</sub> | <sub>$35FF</sub> | <sub>**wasted**</sub> | <sub>$39F8</sub> | <sub>$39FF</sub> | <sub>**wasted**</sub> | <sub>$3DF8</sub> | <sub>$3DFF</sub> |
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| <sub>**32**</sub> | <sub>$2200</sub> | <sub>$2227</sub> | <sub>**33**</sub> | <sub>$2600</sub> | <sub>$2627</sub> | <sub>**34**</sub> | <sub>$2A00</sub> | <sub>$2A27</sub> | <sub>**35**</sub> | <sub>$2E00</sub> | <sub>$2E27</sub> | <sub>**36**</sub> | <sub>$3200</sub> | <sub>$3227</sub> | <sub>**37**</sub> | <sub>$3600</sub> | <sub>$3627</sub> | <sub>**38**</sub> | <sub>$3A00</sub> | <sub>$3A27</sub> | <sub>**39**</sub> | <sub>$3E00</sub> | <sub>$3E27</sub> |
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| <sub>**96**</sub> | <sub>$2228</sub> | <sub>$224F</sub> | <sub>**97**</sub> | <sub>$2628</sub> | <sub>$264F</sub> | <sub>**98**</sub> | <sub>$2A28</sub> | <sub>$2A4F</sub> | <sub>**99**</sub> | <sub>$2E28</sub> | <sub>$2E4F</sub> | <sub>**100**</sub> | <sub>$3228</sub> | <sub>$324F</sub> | <sub>**101**</sub> | <sub>$3628</sub> | <sub>$364F</sub> | <sub>**102**</sub> | <sub>$3A28</sub> | <sub>$3A4F</sub> | <sub>**103**</sub> | <sub>$3E28</sub> | <sub>$3E4F</sub> |
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| <sub>**160**</sub> | <sub>$2250</sub> | <sub>$2277</sub> | <sub>**161**</sub> | <sub>$2650</sub> | <sub>$2677</sub> | <sub>**162**</sub> | <sub>$2A50</sub> | <sub>$2A77</sub> | <sub>**163**</sub> | <sub>$2E50</sub> | <sub>$2E77</sub> | <sub>**164**</sub> | <sub>$3250</sub> | <sub>$3277</sub> | <sub>**165**</sub> | <sub>$3650</sub> | <sub>$3677</sub> | <sub>**166**</sub> | <sub>$3A50</sub> | <sub>$3A77</sub> | <sub>**167**</sub> | <sub>$3E50</sub> | <sub>$3E77</sub> |
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| <sub>**wasted**</sub> | <sub>$2278</sub> | <sub>$227F</sub> | <sub>**wasted**</sub> | <sub>$2678</sub> | <sub>$267F</sub> | <sub>**wasted**</sub> | <sub>$2A78</sub> | <sub>$2A7F</sub> | <sub>**wasted**</sub> | <sub>$2E78</sub> | <sub>$2E7F</sub> | <sub>**wasted**</sub> | <sub>$3278</sub> | <sub>$327F</sub> | <sub>**wasted**</sub> | <sub>$3678</sub> | <sub>$367F</sub> | <sub>**wasted**</sub> | <sub>$3A78</sub> | <sub>$3A7F</sub> | <sub>**wasted**</sub> | <sub>$3E78</sub> | <sub>$3E7F</sub> |
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| <sub>**40**</sub> | <sub>$2280</sub> | <sub>$22A7</sub> | <sub>**41**</sub> | <sub>$2680</sub> | <sub>$26A7</sub> | <sub>**42**</sub> | <sub>$2A80</sub> | <sub>$2AA7</sub> | <sub>**43**</sub> | <sub>$2E80</sub> | <sub>$2EA7</sub> | <sub>**44**</sub> | <sub>$3280</sub> | <sub>$32A7</sub> | <sub>**45**</sub> | <sub>$3680</sub> | <sub>$36A7</sub> | <sub>**46**</sub> | <sub>$3A80</sub> | <sub>$3AA7</sub> | <sub>**47**</sub> | <sub>$3E80</sub> | <sub>$3EA7</sub> |
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| <sub>**104**</sub> | <sub>$22A8</sub> | <sub>$22CF</sub> | <sub>**105**</sub> | <sub>$26A8</sub> | <sub>$26CF</sub> | <sub>**106**</sub> | <sub>$2AA8</sub> | <sub>$2ACF</sub> | <sub>**107**</sub> | <sub>$2EA8</sub> | <sub>$2ECF</sub> | <sub>**108**</sub> | <sub>$32A8</sub> | <sub>$32CF</sub> | <sub>**109**</sub> | <sub>$36A8</sub> | <sub>$36CF</sub> | <sub>**110**</sub> | <sub>$3AA8</sub> | <sub>$3ACF</sub> | <sub>**111**</sub> | <sub>$3EA8</sub> | <sub>$3ECF</sub> |
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| <sub>**168**</sub> | <sub>$22D0</sub> | <sub>$22F7</sub> | <sub>**169**</sub> | <sub>$26D0</sub> | <sub>$26F7</sub> | <sub>**170**</sub> | <sub>$2AD0</sub> | <sub>$2AF7</sub> | <sub>**171**</sub> | <sub>$2ED0</sub> | <sub>$2EF7</sub> | <sub>**172**</sub> | <sub>$32D0</sub> | <sub>$32F7</sub> | <sub>**173**</sub> | <sub>$36D0</sub> | <sub>$36F7</sub> | <sub>**174**</sub> | <sub>$3AD0</sub> | <sub>$3AF7</sub> | <sub>**175**</sub> | <sub>$3ED0</sub> | <sub>$3EF7</sub> |
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| <sub>**wasted**</sub> | <sub>$22F8</sub> | <sub>$22FF</sub> | <sub>**wasted**</sub> | <sub>$26F8</sub> | <sub>$26FF</sub> | <sub>**wasted**</sub> | <sub>$2AF8</sub> | <sub>$2AFF</sub> | <sub>**wasted**</sub> | <sub>$2EF8</sub> | <sub>$2EFF</sub> | <sub>**wasted**</sub> | <sub>$32F8</sub> | <sub>$32FF</sub> | <sub>**wasted**</sub> | <sub>$36F8</sub> | <sub>$36FF</sub> | <sub>**wasted**</sub> | <sub>$3AF8</sub> | <sub>$3AFF</sub> | <sub>**wasted**</sub> | <sub>$3EF8</sub> | <sub>$3EFF</sub> |
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| <sub>**48**</sub> | <sub>$2300</sub> | <sub>$2327</sub> | <sub>**49**</sub> | <sub>$2700</sub> | <sub>$2727</sub> | <sub>**50**</sub> | <sub>$2B00</sub> | <sub>$2B27</sub> | <sub>**51**</sub> | <sub>$2F00</sub> | <sub>$2F27</sub> | <sub>**52**</sub> | <sub>$3300</sub> | <sub>$3327</sub> | <sub>**53**</sub> | <sub>$3700</sub> | <sub>$3727</sub> | <sub>**54**</sub> | <sub>$3B00</sub> | <sub>$3B27</sub> | <sub>**55**</sub> | <sub>$3F00</sub> | <sub>$3F27</sub> |
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| <sub>**112**</sub> | <sub>$2328</sub> | <sub>$234F</sub> | <sub>**113**</sub> | <sub>$2728</sub> | <sub>$274F</sub> | <sub>**114**</sub> | <sub>$2B28</sub> | <sub>$2B4F</sub> | <sub>**115**</sub> | <sub>$2F28</sub> | <sub>$2F4F</sub> | <sub>**116**</sub> | <sub>$3328</sub> | <sub>$334F</sub> | <sub>**117**</sub> | <sub>$3728</sub> | <sub>$374F</sub> | <sub>**118**</sub> | <sub>$3B28</sub> | <sub>$3B4F</sub> | <sub>**119**</sub> | <sub>$3F28</sub> | <sub>$3F4F</sub> |
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| <sub>**176**</sub> | <sub>$2350</sub> | <sub>$2377</sub> | <sub>**177**</sub> | <sub>$2750</sub> | <sub>$2777</sub> | <sub>**178**</sub> | <sub>$2B50</sub> | <sub>$2B77</sub> | <sub>**179**</sub> | <sub>$2F50</sub> | <sub>$2F77</sub> | <sub>**180**</sub> | <sub>$3350</sub> | <sub>$3377</sub> | <sub>**181**</sub> | <sub>$3750</sub> | <sub>$3777</sub> | <sub>**182**</sub> | <sub>$3B50</sub> | <sub>$3B77</sub> | <sub>**183**</sub> | <sub>$3F50</sub> | <sub>$3F77</sub> |
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| <sub>**wasted**</sub> | <sub>$2378</sub> | <sub>$237F</sub> | <sub>**wasted**</sub> | <sub>$2778</sub> | <sub>$277F</sub> | <sub>**wasted**</sub> | <sub>$2B78</sub> | <sub>$2B7F</sub> | <sub>**wasted**</sub> | <sub>$2F78</sub> | <sub>$2F7F</sub> | <sub>**wasted**</sub> | <sub>$3378</sub> | <sub>$337F</sub> | <sub>**wasted**</sub> | <sub>$3778</sub> | <sub>$377F</sub> | <sub>**wasted**</sub> | <sub>$3B78</sub> | <sub>$3B7F</sub> | <sub>**wasted**</sub> | <sub>$3F78</sub> | <sub>$3F7F</sub> |
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| <sub>**56**</sub> | <sub>$2380</sub> | <sub>$23A7</sub> | <sub>**57**</sub> | <sub>$2780</sub> | <sub>$27A7</sub> | <sub>**58**</sub> | <sub>$2B80</sub> | <sub>$2BA7</sub> | <sub>**59**</sub> | <sub>$2F80</sub> | <sub>$2FA7</sub> | <sub>**60**</sub> | <sub>$3380</sub> | <sub>$33A7</sub> | <sub>**61**</sub> | <sub>$3780</sub> | <sub>$37A7</sub> | <sub>**62**</sub> | <sub>$3B80</sub> | <sub>$3BA7</sub> | <sub>**63**</sub> | <sub>$3F80</sub> | <sub>$3FA7</sub> |
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| <sub>**120**</sub> | <sub>$23A8</sub> | <sub>$23CF</sub> | <sub>**121**</sub> | <sub>$27A8</sub> | <sub>$27CF</sub> | <sub>**122**</sub> | <sub>$2BA8</sub> | <sub>$2BCF</sub> | <sub>**123**</sub> | <sub>$2FA8</sub> | <sub>$2FCF</sub> | <sub>**124**</sub> | <sub>$33A8</sub> | <sub>$33CF</sub> | <sub>**125**</sub> | <sub>$37A8</sub> | <sub>$37CF</sub> | <sub>**126**</sub> | <sub>$3BA8</sub> | <sub>$3BCF</sub> | <sub>**127**</sub> | <sub>$3FA8</sub> | <sub>$3FCF</sub> |
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||||
| <sub>**184**</sub> | <sub>$23D0</sub> | <sub>$23F7</sub> | <sub>**185**</sub> | <sub>$27D0</sub> | <sub>$27F7</sub> | <sub>**186**</sub> | <sub>$2BD0</sub> | <sub>$2BF7</sub> | <sub>**187**</sub> | <sub>$2FD0</sub> | <sub>$2FF7</sub> | <sub>**188**</sub> | <sub>$33D0</sub> | <sub>$33F7</sub> | <sub>**189**</sub> | <sub>$37D0</sub> | <sub>$37F7</sub> | <sub>**190**</sub> | <sub>$3BD0</sub> | <sub>$3BF7</sub> | <sub>**191**</sub> | <sub>$3FD0</sub> | <sub>$3FF7</sub> |
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|
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This structure might seem confusing and it's true that most of the time programmers will use lookup tables to find the starting address of a line instead of using the above formula.
|
||||
|
||||
Nonetheless, even such an interlaced structure could be used without resorting to lookup tables, depending on the use case.
|
||||
|
||||
For example, if we're on a line that's a multiple of 8 (that's the first 3 columns in the table above), all we have to do to find the address of the 8 next lines is to add 1 to the most significant byte (MSB) of the address.
|
||||
|
||||
For instance, if we draw bitmaps starting from a line that is a multiple of 8, like it might be the case when displaying tiles in a game, we only need the address of the first line, while the address of the other lines have the same LSB but an MSB that is incremented by one each time.
|
||||
|
||||
Another example is when you write a fast routine to clear the hires screen. You'll want to skip the hires holes for two reasons:
|
||||
1. It's 512 bytes that don't need to be cleared and that will waste cycles
|
||||
2. You may want to use these 512 bytes to store data and so you don't want to erase it
|
||||
|
||||
The position of the screen holes is also very regular. First they are all within the third section of the screen. Then their address range is either `$xx78-$xx7F` or `$xxF8-$xxFF`.
|
||||
|
||||
We make use of this information by looping down from `#$F7` (thus skipping the second kind of hole area) to `#$00` but skipping to `#$77` once we reach `#$7F`.
|
||||
|
|
|
|||
Loading…
Reference in New Issue
Block a user