HCS360_01 Datasheet, PDF (10/28 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder

HCS360
3.5.10 MANCH: MANCHESTER CODE
MODULATION
MANCH selects between Manchester code modulation
and PWM modulation. If MANCH = 1, Manchester code
modulation is selected:
If MANCH = 0, PWM modulation is selected.
3.5.11 OVR: OVERFLOW
The overflow bit is used to extend the number of possi-
ble synchronization values. The synchronization
counter is 16 bits in length, yielding 65,536 values
before the cycle repeats. Under typical use of
10 operations a day, this will provide nearly 18 years of
use before a repeated value will be used. Should the
system designer conclude that is not adequate, then
the overflow bit can be utilized to extend the number of
unique values. This can be done by programming OVR
to 1 at the time of production. The encoder will auto-
matically clear OVR the first time that the transmitted
synchronization value wraps from 0xFFFF to 0x0000.
Once cleared, OVR cannot be set again, thereby creat-
ing a permanent record of the counter overflow. This
prevents fast cycling of 64K counter. If the decoder sys-
tem is programmed to track the overflow bits, then the
effective number of unique synchronization values can
be extended to 128K. If programmed to zero, the sys-
tem will be compatible with the NTQ104/5/6 devices
(i.e., no overflow with discrimination bits set to zero).
4.0 TRANSMITTED WORD
4.1 Transmission Format (PWM)
The HCS360 transmission is made up of several parts
(Figure 4-1 and Figure 4-2). Each transmission is
begun with a preamble and a header, followed by the
encrypted and then the fixed data. The actual data is
67 bits which consists of 32 bits of encrypted data and
35 bits of fixed data. Each transmission is followed by
a guard period before another transmission can begin.
Refer to Table 8-4 and Table 8-5 for transmission tim-
ing specifications. The encrypted portion provides up to
four billion changing code combinations and includes
the function bits (based on which buttons were acti-
vated) along with the synchronization counter value
and discrimination value. The non-encrypted portion is
comprised of the CRC bits, VLOW bits, the function bits
and the 28/32-bit serial number. The encrypted and
non-encrypted sections combined increase the number
of combinations to 1.47 x 10²⁰.
4.2 Code Word Organization
The HCS360 transmits a 67-bit code word when a but-
ton is pressed. The 67-bit word is constructed from a
Fixed Code portion and an Encrypted Code portion
(Figure 4-3).
The Encrypted Data is generated from 4 function bits,
2 user bits, overflow bit, independent mode bit, and 8
serial number bits, and the 16-bit synchronization value
(Figure 8-4).
The Non-encrypted Code Data is made up of a VLOW
bit, 2 CRC bits, 4 function bits, and the 28-bit serial
number. If the extended serial number (32 bits) is
selected, the 4 function code bits will not be transmit-
ted.
DS40152D-page 10
 2001 Microchip Technology Inc.