di2838l1.txt
;***************************************************************************************************
; DECODING PROGRAM
;
; "Hints and kinks for USB decoding," EDN, Feb 7, 2002, pg 108
;
;***************************************************************************************************

'NRZI.bas codes and decodes a binary data sequence to NRZI and conversely
'Be careful how the NOT function is used.  NOT b(i) is 2 + NOT b(i) !!!

'              Binary vs Differential Code Combinations
'           ______________________________________________
'          |    Binary                Differential        |
'          | b(n-1)  b(n)    d(n-1)  d(n) or d(n-1)  d(n) |
'          |   0      0        1      0        0       1  |
'          |   0      1        0      0        1       1  |
'          |   1      0        0      1        1       0  |
'          |   1      1        1      1        0       0  |
'           ----------------------------------------------
'd(n) = D+ polarity. To convert from differential d(n) to binary b(n):
'If d(n-1) <> d(n), then b(n) = 0. If d(n-1) = d(n), then b(n) = 1, or
'b(n) = d(n) XOR NOT d(n-1). To convert from binary to differential:
'If b(n) = 1, then d(n) = d(n-1). If b(n) = 0, then d(n) = NOT d(n-1).
'Check soln: d(n) = 1  0  0  0  1  1  0  0  1  0  1  1  0  1  1  1
'            b(n) = 1  0  1  1  0  1  0  1  0  0  0  1  0  0  1  1
            
CLS : DIM b(16) AS INTEGER, d(16) AS INTEGER
PRINT "If you want to convert binary to NRZI data press ENTER"
INPUT "If you want to convert NRZI to binary data enter 1  ", a%
IF a% = 1 GOTO 100
PRINT "Enter 16 binary data digits and press ENTER after each one"
PRINT " i   B"
FOR i = 0 TO 15
        PRINT i; : INPUT b(i)
        NEXT i
        INPUT "Enter an initial binary digit for d(0)  ", d(0)
        CLS : PRINT "B ="; SPC(1); b(0);
FOR i = 1 TO 15
        PRINT SPC(1); b(i);
        d(i) = d(i - 1)
        IF b(i) = 0 THEN d(i) = 2 + NOT d(i - 1)
        NEXT i
        PRINT : PRINT : PRINT "D ="; SPC(1); d(0);
FOR i = 1 TO 15
        PRINT SPC(1); d(i);
        NEXT i
END
100     PRINT "Enter 16 NRZI data digits and press ENTER after each one"
        PRINT " i   D"
FOR i = 0 TO 15
        PRINT i; : INPUT d(i)
        NEXT i
        INPUT "Enter an initial binary digit for b(0) ", b(0)
        CLS : PRINT "D ="; SPC(1); d(0);
FOR i = 1 TO 15
        PRINT SPC(1); d(i);
    '    IF d(i) = d(i - 1) THEN b(i) = 1
    '    IF d(i) <> d(i - 1) THEN b(i) = 0
        b(i) = d(i) XOR (2 + NOT d(i - 1))
        NEXT i
PRINT : PRINT : PRINT "B ="; SPC(1); b(0);
FOR i = 1 TO 15
        PRINT SPC(1); b(i);
        NEXT i