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HCS360 Datasheet, PDF (10/24 Pages) Microchip Technology – KEELOQ CODE HOPPING ENCODER | |||
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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 overï¬ow 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 overï¬ow 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 automat-
ically clear OVR the ï¬rst time that the transmitted syn-
chronization value wraps from 0xFFFF to 0x0000.
Once cleared, OVR cannot be set again, thereby creat-
ing a permanent record of the counter overï¬ow. This
prevents fast cycling of 64K counter. If the decoder sys-
tem is programmed to track the overï¬ow 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 overï¬ow 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 ï¬xed data. The actual data is
67 bits which consists of 32 bits of encrypted data and
35 bits of ï¬xed 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 timing
speciï¬cations. 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, overï¬ow 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.
DS40152C-page 10
Preliminary
© 1996 Microchip Technology Inc.
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