MagTek TTL - Manual (Page 9)

Section 1. Decoding Reader Output
5
1. "00.00"
leading clocking zeros Approximately 22 (tk2) or 62 (tk3)
2. "11010" the character "hex B" (01011) the Start Sentinel
3. "10000" the character "1" (00001)
4. "01000" the character "2" (00010)
5. "11001" the character "3" (10011)
6. "11111" the character "hex F" (11111) the End Sentinel
7. "00100" the character "4" (00100) the LRC (check digit)
8. "00.00" trailing clocking zeros A minimum of 22 (Tk2) or 62 (tk3)
to the end of the card
Calculating odd parity and LRC for the message 123:
P 8 4 2 1 Hex Value Decimal Value
Less Parity Less Parity
Start Sentinel: B
0 1 0 1 1 B 11 (8+2+1)
1 0 0 0 0 1 1 1
2 0 0 0 1 0 2 2
3 1 0 0 1 1 3 3 (2+1)
End Sentinel: F 1 1 1 1 1 F 15 (8+4+2+1)
___________ __
LRC 4 0 0 1 0 0 4 4
Calculating odd parity: scan each horizontal row and enter a zero or one In the P column so that
each row has an odd number of one's.
To find the LCR: disregard the parity bits, scan up each vertical column, and make sure that each
column has a even number of one's in it. Enter a zero or one in the LCR position, so that it does.
If you are using a computer to calculate the LCR, use the "exclusive or" function. Next, calculate
odd parity for the LCR character, in the horizontal direction.
The Hex characters are usually displayed in their ASCII equivalent: Hex B as a ";" semicolon,
Hex D as an "=" equal sign, and Hex F as a "?" question mark.