PN#
500-12300
Page
4
Rev. C, 6/09
the unusual case where both keypads are being used simultaneously, the code will not be
properly sent as the sequence will certainly be disturbed. Only one keypad may be used at a
time. Be sure you don’t violate egress building codes when employing a keypad on the
inside of a door. Check with your local building or fire department.
APPENDIX A: 2601 CODE STRUCTURE
The 26 bit transmission begins with a parity bit followed by 24 code bits and ended by a second
parity bit. The first parity bit is even parity calculated over the first 12 code bits as follows: if
the 12 bits sum to 0, the parity bit is set to 0. If the 12 bits sum to 1, the parity bit is set to 1.
The second (ending) parity bit is odd parity calculated over the second 12 code bits as follows: if
the second 12 bits sum to 0, the parity bit is set to 1. If the second 12 bits sum to 1, the parity
bit is set to 0.
The 24 code bits have internal structure as follows. The first eight bits are the facility code. The
next 16 bits are the PIN code. All data is transmitted Most Significant Bit first from the keypad.
The transmission begins with the even parity bit, proceeds through the eight bit facility code
followed by the 16 bit PIN code and ends with the odd parity bit.
The transmission of a 0 bit occurs when the data 0 line transitions below 1.1 V for 50
microseconds. The transmission of a 1 bit occurs when the data 1 line transitions below 1.1 V for
50 microseconds. The interval between bit transmitting pulses is one millisecond.
