Acorn Computers BBC Micro Model B w/8271 — Acorn BBC Micro Model B w/8271 User Guide Manual PDF

134 To make these display as graphics characters each line must be preceded by (for example) code 146 (green graphics). So the following codes must be printed on the screen:

146, 250, 245 146, 255, 255 146, 191, 239 These codes can be sent using PRINT CHR$( ) as long as you are careful to get each code in the correct place, eg 10 MODE 7 20 X=20 30 Y=10 40 PRINT TAB(X,Y);CHR$(146);CHR$(154);CHR$(250);CHR$(245) 50 PRINT TAB(X,Y+1);CHR$(146);CHR$(154);CHR$(255);CHR$(255) 60 PRINT TAB(X,Y+2);CHR$(146);CHR$(154);CHR$(191);CHR$(239) Instead of using PRINT TAB (X,Y) it is probably easier in this case to use ASCII codes to move the cursor-down one line (code 10 ) and back four spaces (code 8 four times). It is probably also easier to use the VDU statement rather than PRINT CHR$ ( ) .

If these two things are done then the program becomes 5 MODE 7 6 PRINT TAB(20,10); 10 VDU 146,154,250,245 20 VDU 10,8,8,8,8 30 VDU 146,154,255,255 40 VDU 10,8,8,8,8 50 VDU 146,154,191,239 100 PRINT A complete list of the Teletext codes is given in Appemdix A and Appendix B. Teletext graphics codes for the more adventurous As you will have realised, the statements MOVE and DRAW are not available in the Teletext mode( MODE 7 ). If you wish to draw lines in this mode you will need to use a suitable procedure – so here is one. It uses a look-up table, called S% , to remember the numbers corresponding to each of the six pixels (picture elements) in a Teletext graphics character.

The look-up table must be set up at the beginning of the program: