HCS361_11 Datasheet, PDF (8/42 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder incorporates high security,

HCS361
3.5.6
BACW: BLANK ALTERNATE CODE
WORD
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 transmit a higher peak power (see
Section 5.2).
3.5.7
XSER: EXTENDED SERIAL
NUMBER
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.
Note:
Since the button status S[3:0] is used to
detect a Seed transmission, Extended
Serial Number and Secure Learn are
mutually exclusive.
FIGURE 3-2:
CODE WORD ORGANIZATION
XSER=0
Fixed Code Portion of Transmission
CRC
(2-bit)
MSB
VLOW
(1-bit)
Button
Status
(4 bits)
28-bit
Serial Number
XSER=1
Fixed Code Portion of Transmission
CRC
(2-bit)
MSB
VLOW
(1-bit)
32-bit
Extended Serial Number
3.5.8 DISCRIMINATION VALUE
While in other KEELOQ encoders its value is user
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
USRA,B: USER BITS
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.
Encrypted Portion of Transmission
Button
Status
(4 bits)
Discrimination
bits
(12 bits)
16-bit
Sync Value
LSB
67 bits
of Data
Transmitted
Encrypted Portion of Transmission
Button
Status
(4 bits)
Discrimination
bits
(12 bits)
16-bit
Sync Value
LSB
Button Status
(4 bits)
SS S S
21 0 3
Discrimination Bits
(12 bits)
I O U U S S ... S
N V S S E E ... E
D R R R R R ... R
1 0 7 6 ... 0
DS40146F-page 8
© 2011 Microchip Technology Inc.