BACKTAB

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Short for BACKground TABle, this is an area of memory that defines the "Background" of the screen. The STIC defines the BACKTAB's format.

The BACKTAB occupies 240 words of System RAM starting at location $0200 and ending at location $02EF. It forms a 20 column by 12 row grid for character tiles, also known as "cards." Each character tile is 8 pixels by 8 pixels. The following image from the Hello World Tutorial illustrates how the BACKTAB is divided into rows and colums:

Hello1 scrshot grid.gif


The following table shows how rows and columns map to addresses. Display address locations are also given by the formula $0200 + row*20 + column, with row 0 indicating the topmost row, and column 0 indicating the leftmost column.

 Col 
0
 Col 
1
 Col 
2
 Col 
3
 Col 
4
 Col 
5
 Col 
6
 Col 
7
 Col 
8
 Col 
9
 Col 
10
 Col 
11
 Col 
12
 Col 
13
 Col 
14
 Col 
15
 Col 
16
 Col 
17
 Col 
18
 Col 
19
  Row  
0
$0200$0201$0202$0203 $0204$0205$0206$0207 $0208$0209$020A$020B $020C$020D$020E$020F $0210$0211$0212$0213
  Row  
1
$0214$0215$0216$0217 $0218$0219$021A$021B $021C$021D$021E$021F $0220$0221$0222$0223 $0224$0225$0226$0227
  Row  
2
$0228$0229$022A$022B $022C$022D$022E$022F $0230$0231$0232$0233 $0234$0235$0236$0237 $0238$0239$023A$023B
  Row  
3
$023C$023D$023E$023F $0240$0241$0242$0243 $0244$0245$0246$0247 $0248$0249$024A$024B $024C$024D$024E$024F
  Row  
4
$0250$0251$0252$0253 $0254$0255$0256$0257 $0258$0259$025A$025B $025C$025D$025E$025F $0260$0261$0262$0263
  Row  
5
$0264$0265$0266$0267 $0268$0269$026A$026B $026C$026D$026E$026F $0270$0271$0272$0273 $0274$0275$0276$0277
  Row  
6
$0278$0279$027A$027B $027C$027D$027E$027F $0280$0281$0282$0283 $0284$0285$0286$0287 $0288$0289$028A$028B
  Row  
7
$028C$028D$028E$028F $0290$0291$0292$0293 $0294$0295$0296$0297 $0298$0299$029A$029B $029C$029D$029E$029F
  Row  
8
$02A0$02A1$02A2$02A3 $02A4$02A5$02A6$02A7 $02A8$02A9$02AA$02AB $02AC$02AD$02AE$02AF $02B0$02B1$02B2$02B3
  Row  
9
$02B4$02B5$02B6$02B7 $02B8$02B9$02BA$02BB $02BC$02BD$02BE$02BF $02C0$02C1$02C2$02C3 $02C4$02C5$02C6$02C7
  Row  
10
$02C8$02C9$02CA$02CB $02CC$02CD$02CE$02CF $02D0$02D1$02D2$02D3 $02D4$02D5$02D6$02D7 $02D8$02D9$02DA$02DB
  Row  
11
$02DC$02DD$02DE$02DF $02E0$02E1$02E2$02E3 $02E4$02E5$02E6$02E7 $02E8$02E9$02EA$02EB $02EC$02ED$02EE$02EF
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