hcs412 Microchip Technology Inc., hcs412 Datasheet - Page 10

• Manufacturer Part Number: hcs412
• Description: Keeloq? Code Hopping Encoder And Transponder
• Manufacturer: Microchip Technology Inc.

HCS412
FIGURE 3-2:
3.2.1
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 (T
pressed again) within the Queue Time (T
FIGURE 3-3:
DS41099C-page 10
Code Words
Transmitted
28-bit Serial Number (XSER = 0)
32-bit Serial Number (XSER = 1)
MSb
MSb
Q1 Q0 C1 C0
Q1 Q0 C1 C0
2 Bits
2 Bits
QUE
QUE
Shaded data included in CRC calculation
QUEUE COUNTER (QUE)
Input
Sx
2 Bits
2 Bits
CRC
CRC
CODE WORD ORGANIZATION
QUE COUNTER TIMING DIAGRAM
V
V
1-Bit
1-Bit
t
LOW
1
LOW
Fixed Code Portion (37 Bits)
DBR
Fixed Code Portion (37 Bits)
S2
= 0
), then reactivated (button
S1 S0 LC0
4 Bits
BUT
Most Sig 16 Bits
1st Button Press
SER 1
12 MSb’s
SER 1
Synch CNT = X
QUE1:0 = 00
QUE
). The
t
1
Least Sig 16 Bits
Least Sig16 Bits
> T
Preliminary
2
DBP
SER 0
SER 0
t
2
= 0
S2
S2
S1 S0 LC0 OVR1
S1 S0 LC0 OVR1
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 (T
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 (T
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
4 Bits
4 Bits
BUT
BUT
QUE
Hopping Code Portion Message (32 Bits)
Hopping Code Portion Message (32 Bits)
Overflow
Overflow
) apart.
Counter
Counter
2 Bits
2 Bits
T
DISCRIM
DISCRIM
DBR
10 Bits
OVR0
10 Bits
OVR0
< t < T
2002 Microchip Technology Inc.
QUE
15
QUE
15
Transmitted LSb first.
Transmitted LSb first.
) then initiates a new
2nd Button Press
Synchronization
Synchronization
Synch CNT = X+1
69 Data bits
69 Data bits
QUE1:0 = 01
Counter
Counter
16 Bits
16 Bits
LSb
LSb
2
0
0