BACKTAB
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:
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 |
