HCS412_11 Datasheet, PDF (10/52 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder and Transponder Burglar alarm systems

HCS412
FIGURE 3-2: CODE WORD ORGANIZATION
28-bit Serial Number (XSER = 0)
Fixed Code Portion (37 Bits)
QUE CRC
2 Bits 2 Bits ^VLOW
1-Bit
Q1 Q0 C1 C0
BUT
4 Bits
SER 1
12 MSb’s
MSb
S2 S1 S0 LC0
32-bit Serial Number (XSER = 1)
Hopping Code Portion Message (32 Bits)
SER 0
Least Sig16 Bits
BUT
4 Bits
Counter
Overflow
2 Bits
DISCRIM
10 Bits
Synchronization
Counter
16 Bits
15
0
S2 S1 S0 LC0 OVR1 OVR0
LSb
69 Data bits
Transmitted LSb first.
Fixed Code Portion (37 Bits)
Hopping Code Portion Message (32 Bits)
QUE CRC
2 Bits 2 Bits ^VLOW
1-Bit
Q1 Q0 C1 C0
MSb
SER 1
Most Sig 16 Bits
SER 0
Least Sig 16 Bits
BUT
4 Bits
Counter
Overflow
2 Bits
DISCRIM
10 Bits
Synchronization
Counter
16 Bits
15
0
S2 S1 S0 LC0 OVR1 OVR0
LSb
Shaded data included in CRC calculation
69 Data bits
Transmitted LSb first.
3.2.1 QUEUE COUNTER (QUE)
The QUE counter can be used to request secondary
decoder functions using only a single transmitter but-
ton. Typically a decoder must keep track of incoming
transmissions to determine when a double button press
occurs, perhaps an unlock all doors request. The QUE
counter removes this burden from the decoder by
counting multiple button presses.
The 2-bit QUE counter is incremented each time an
active button input is released for at least the
Debounce Time (TDBR), then reactivated (button
pressed again) within the Queue Time (TQUE). The
FIGURE 3-3: QUE COUNTER TIMING DIAGRAM
1st Button Press
Input
Sx
counter increments up from 0 to a maximum of 3,
returning to 0 only after a different button activation or
after button activations spaced greater than the Queue
Time (TQUE) apart.
The current transmission aborts, after completing the
minimum number of code words (Section 3.4.1), when
the active button input is released. A button re-activa-
tion within Queue Time (TQUE) then initiates a new
transmission (new synchronization counter, encrypted
data) using the updated QUE value.
Figure 3-3 shows the timing diagram to increment the
queue counter value.
All Buttons Released
2nd Button Press
Code Words
Transmitted
t₁ = 0
QUE1:0 = 00₂
Synch CNT = X
t₁ > TDBP
t₂ = 0
QUE1:0 = 01₂
Synch CNT = X+1
TDBR < t < TQUE
DS41099D-page 10
© 2011 Microchip Technology Inc.