' KCTS TassyJim Sep 2022
 OPTION EXPLICIT
 OPTION DEFAULT INTEGER
 DIM bits(10), message$
 DIM FLOAT rxd(200), bt!
 DIM starttime!, midtime!
 DIM n, done, k$, char$
 CONST bit_time = 3.1      ' should be 3.33 less processing time.
 CONST char_timeout = 37.0 ' one character takes ~36mS
 CONST char_time = 12.0    ' at 250k CPU it takes ~10 mS to process one character
 CONST bit_choice = 1.2    ' this is the time for two cycles half way between 1200 and 2400 Hz
 CONST dir_mode = 1        ' 1 = sending, 0 = receiving
 
 IF dir_mode THEN ' we are sending text
   message$ = "Hello world"
   sendtxt message$
     PAUSE 2000
   DO
     k$ = INKEY$
     IF k$ <> "" THEN
       sendtxt k$
     ENDIF
   LOOP
 ELSE       ' we are receiving text
   SETPIN gp15, INTH, startrec
   SETPIN gp14, DOUT ' used for timing on the CRO
   
   DO
     IF done = 1 THEN ' we have finished receiving a character
       done = 0
       PIN(gp14) = 1 ' used for timing measurements
       char$ = recchar$()
       PRINT char$;
       SETPIN gp15, INTH, startrec ' arm the interrupt ready for the next character
       PIN(gp14) = 0
     ENDIF
   LOOP
   
 ENDIF
 
 
' routines used for receiving and decoding KCTS
 
' parse the array of received timing and extract the 8 bit byte
FUNCTION recchar$()
 LOCAL b, char_asc
 bt! = bit_time/1.8 ' take the first sample shortly after half way throug it.
 b = 0
 FOR n = 1 TO 100
   IF rxd(n) = 0 THEN : EXIT FOR : ENDIF
'print str$(n,5);"  ";str$(rxd(n)*1000,6,1);"  ";str$((rxd(n)-rxd(n-1))*1000,6,1)
   IF rxd(n) > bt! THEN
     IF (rxd(n)-rxd(n-2)) < bit_choice THEN ' we average over two cycles
       bits(b) = 1
     ELSE
       bits(b) = 0
     ENDIF
' print bits(b), (rxd(n)-rxd(n-2)), b,  bt!
     bt! = bt! + bit_time
     INC b
   ENDIF
 NEXT n
 FOR n = 8 TO 1 STEP -1
   char_asc = (char_asc << 1) + bits(n) ' lsb received first
 NEXT n
 MATH set 0, rxd()   ' finished with it so clear the array
 recchar$ = CHR$(char_asc)
END FUNCTION
 
' arm the interrupt and timeout
' reset the data array pointer
SUB startrec
 done = 0
 n = 1
 TIMER = 0
 SETTICK char_timeout, stoprec,1
 SETPIN gp15, INTH, getdata_int
END SUB
 
' disable interupts and set the done flag
SUB stoprec
 SETPIN gp15, OFF
 SETTICK 0,0,1
 done = 1
END SUB
 
' get the time of the next cycle and advance the counter
SUB getdata_int
 rxd(n) = TIMER
 INC n
END SUB
 
' these two subs are all thats needed to send text
SUB sendtxt txt$
 LOCAL n
 IF LEN(txt$) > 0 THEN
   FOR n = 1 TO LEN(txt$)
     sendchar MID$(txt$,n,1)
     PAUSE char_time
   NEXT n
 ENDIF
END SUB
 
SUB sendchar ch$
 LOCAL n
 bits(0) = 0                      ' start bit
 FOR n = 1 TO 8
   bits(n) = (ASC(ch$) >>(n-1)) AND 1 ' bits sent lsb first
 NEXT n
 bits(9) = 1                      ' 2 stop bits
 bits(10) = 1
 FOR n = 0 TO 10
   PLAY TONE 1200*(bits(n)+1),1200*(bits(n)+1) ' 0 = 1200, 1 = 2400
   PAUSE bit_time
 NEXT n
 PLAY STOP
END SUB