hcs361 Microchip Technology Inc., hcs361 Datasheet - Page 8

• Manufacturer Part Number: hcs361
• Description: Keeloq Code Hopping Encoder
• Manufacturer: Microchip Technology Inc.

HCS361
3.5.6
BACW = 1 selects the encoder to transmit every sec-
ond code word. This can be used to reduce the aver-
age power transmitted over a 100 ms window and
thereby
Section 5.2).
3.5.7
If XSER = 0, the four Most Significant bits of the Serial
Number are substituted by S[3:0] and the code word
format is compatible with the HCS200/300/301.
If XSER = 1, the full 32-bit Serial Number [SER_1,
SER_0] is transmitted.
FIGURE 3-2:
DS40146E-page 8
Note:
XSER=0
MSB
XSER=1
MSB
(2-bit)
transmit
CRC
(2-bit)
Since the button status S[3:0] is used to
detect a Seed transmission, Extended
Serial Number and Secure Learn are
mutually exclusive.
CRC
BACW: BLANK ALTERNATE CODE
WORD
XSER: EXTENDED SERIAL
NUMBER
Fixed Code Portion of Transmission
Fixed Code Portion of Transmission
(1-bit)
V
(1-bit)
V
LOW
a
LOW
CODE WORD ORGANIZATION
higher
S
2
Button Status
(4 bits)
Button
Status
(4 bits)
S
1
peak
S
Extended Serial Number
0
S
3
power
32-bit
Serial Number
28-bit
(see
N
D
3.5.8
While in other K
selectable, the HCS361 uses directly the 8 Least Sig-
nificant bits of the Serial Number as part of the infor-
mation that form the encrypted portion of the
transmission (Figure 3-2).
The discrimination value aids the post-decryption
check on the decoder end. After the receiver has
decrypted a transmission, the discrimination bits are
checked against the encoder Serial Number to verify
that the decryption process was valid.
3.5.9
User bits form part of the discrimination value. The user
bits together with the IND bit can be used to identify the
counter that is used in Independent mode.
(4 bits)
Button
Status
I
(4 bits)
Button
Status
O
Encrypted Portion of Transmission
V
R
Encrypted Portion of Transmission
Discrimination Bits
U
S
R
1
Discrimination
Discrimination
(12 bits)
DISCRIMINATION VALUE
USRA,B: USER BITS
U
S
R
(12 bits)
0
(12 bits)
bits
bits
S
E
R
7
EE
L
S
E
R
6
OQ
...
...
...
...
encoders its value is user
2002 Microchip Technology Inc.
R
S
E
0
Sync Value
Sync Value
16-bit
16-bit
67 bits
of Data
Transmitted
LSB
LSB