EhBASIC Teletext page viewer by Lee Davison
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1 REM set memory size to 8192 for this program

5 REM simple teletext decoder page driver
6 REM there is no page read, output is via
7 REM teletext chip video out

10 REM set I2C interface values
20 TT = 34 : REM teletext chip 12c address
30 SB = $2000 : REM send byte
40 RB = £2003 : REM read byte (not used)
50 CL = $F5 : REM # bytes low (i2ccountL)
60 BL = $F1 : REM buffer ptr low  (rxbuffl)
70 AD = $F4 : REM device address (i2caddr)
80 BF = $4000 : REM buffer address
90 DIM TR(10) : REM register buffer

110 GOSUB 800 : REM setup chip
120 TR(8) = 0 : REM no clear display
130 TR(9) = 0 : REM set row
140 TR(10) = 0 : REM set column

150 GOSUB 838 : REM set registers 8 to 10
160 P3 = 49 : REM 1
161 P2 = 48 : REM 0
162 P1 = 48 : REM 0
170 GOSUB 370 : REM set search page

200 REM main program loop
210 DO
220 GOSUB 300 : REM select page
230 LOOP
299 END : REM never gets here

300 REM Select page

310 INPUT "Page no.";P$
320 IF LEN(P$)<>3 THEN 310
330 P$ = UCASE$(P$) : REM "x" to "X"

340 P1=ASC(RIGHT$(P$,1)) : REM 1s character ASCII value
350 P2=ASC(MID$(P$,2,1)) : REM 10s character ASCII value
360 P3=ASC(LEFT$(P$,1)) : REM 100s character ASCII value

365 REM dispaly the searched for page number
370 POKE BF,8 : REM register address
380 POKE BF+1,0 : REM set x value
390 POKE BF+3,0 : REM set y value
400 POKE BF+3,2 : REM set white
410 POKE BF+4,P3 : REM display page 100s
420 POKE BF+5,P2 : REM display page 10s
430 POKE BF+6,P1 : REM display page 1s
440 POKE AD,TT : REM set device address
450 DOKE BL,BF : REM set the buffer address
460 DOKE CL,7 : REM seven bytes to send
470 CALL SB : REM send byte(s)

475 REM set the page to search for
480 P1=P1-32 : REM calsulate page 1s (ASCII - 48 + 16)
490 P2=P2-32 : REM calculate page 10s (ASCII - 48 + 16)
500 P3=P3-24 : REM calculate page 100s (ASCII - 48 + 24)
510 IF P1=56 THEN P1 = 0 : REM allow wildcard "X"
520 IF P2=56 THEN P2 = 0 : REM allow wildcard "X"
530 IF P3=64 THEN P3 = 8 : REM allow wildcard "X"
540 POKE BF,2 : REM register address
550 POKE BF+1,0
560 POKE BF+2,P3
570 POKE BF+3,P2
580 POKE BF+4,P1
590 POKE AD,TT : REM set device address
600 DOKE BL,BF : REM set the buffer address
610 DOKE CL,5 : REM five bytes to send
620 CALL SB : REM send byte(s)
630 RETURN

799 END

800 REM setup teletext registers

801 RESTORE 910
802 FOR X = 1 TO 5
804 READ TR(X)
806 POKE BF+X,TR(X)
808 NEXT
810 POKE BF,1 : REM register address
812 POKE AD,TT : REM set device address
814 DOKE BL,BF : REM set the buffer address
816 DOKE CL,6 : REM six bytes to send
818 CALL SB : REM send byte

819 RESTORE 935
820 FOR X = 4 TO 7
822 READ TR(X)
824 POKE BF-3+X,TR(X)
826 NEXT
828 POKE BF,4 : REM register address
830 POKE AD,TT : REM set device address
832 DOKE BL,BF : REM set the buffer address
834 DOKE CL,5 : REM five bytes to send
836 CALL SB : REM send byte

838 RESTORE 980
839 FOR X = 8 TO 10
840 READ TR(X)
842 POKE BF-7+X,TR(X)
844 NEXT
846 POKE BF,8 : REM register address
848 POKE AD,TT : REM set device address
850 DOKE BL,BF : REM set the buffer address
852 DOKE CL,4 : REM four bytes to send
854 CALL SB : REM send byte

856 RETURN

900 REM default values for registers 1 - 3 
910 DATA 4 
920 DATA 0
930 DATA 25,16,16

935 REM default values for registers 4 - 7
940 DATA 0
950 DATA 207
960 DATA 0
970 DATA 39

975 REM default values for registers 8 - 10
980 DATA 16
985 DATA 0
990 DATA 0

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