hcs370 Microchip Technology Inc., hcs370 Datasheet - Page 11

• Manufacturer Part Number: hcs370
• Description: Keeloq Code Hopping Encoder
• Manufacturer: Microchip Technology Inc.

3.2
A K
code data, 32 bits of fixed code data, and between 3 to
5 bits of status information. Various code word formats
are shown in Figure 3-1 and Figure 3-2.
3.2.1
The hopping code portion is calculated by encrypting
the counter, discrimination value, and function code
with the Encoder Key (KEY). The hopping code is cal-
culated when a button press is debounced and remains
unchanged until the next button press.
The synchronization counter can be either a 16- or 20-
bit value. The Configuration Option Counter Select
(CNTSEL) will determine this. The counter select option
must be the same for both Encoder 1 and Encoder 2.
If the 16-bit counter is selected, the discrimination value
is 10 bits long and there are 2 counter overflow bits
(OVR0, OVR1). Set both bits in production and OVR0
will be cleared on the first counter overflow and OVR1 on
the second. Clearing OVR0 with OVR1 set will only
detect the first overflow. Clearing both OVR bits will
effectively give 12 constant bits for discrimination.
If the counter is 20 bits, the discrimination value is 8 bits
long and there are no overflow bits. The rest of the 32
bits are made up of the function code also known as the
button inputs.
The discrimination value can be programmed with any
value to serve as a post decryption check on the
decoder end. In a typical system, this will be pro-
grammed with the 8 or 10 Least Significant bits of the
FIGURE 3-1:
2002 Microchip Technology Inc.
With XSER=1, 16-bit Counter, QUEN=1
With XSER=0, 16-bit Counter, QUEN=0
Q1 Q0 C1 C0
EE
2 Bits
QUE
C1
L
Status Information
Status Information
OQ
2 Bits
CRC
Code Word Format
code word consists of 32 bits of hopping
(3 Bits)
(5 Bits)
HOPPING CODE PORTION
2 Bits
CRC
C0
CODE WORD DATA FORMAT (16-BIT COUNTER)
V
V
1-Bit
1-Bit
LOW
LOW
S2 S1 S0 S3
4 Bits
BUT
Fixed Code Portion (32 Bits)
Fixed Code Portion (32 Bits)
SERIAL NUMBER
SERIAL NUMBER
(32 Bits)
(28 Bits)
Preliminary
S2
S2
S1
S1
serial number. This will be stored by the receiver sys-
tem after a transmitter has been learned. The discrimi-
nation bits are part of the information that is to form the
encrypted portion of the transmission.
3.2.2
The 32 bits of fixed code consist of 28 bits of the serial
number (SER) and a copy of the 4-bit function code.
This can be changed to contain the whole 32-bit serial
number by setting the Extended Serial Number (XSER)
configuration option to a 1. If more than one button is
pressed, the function codes are logically OR’ed
together. The function code is repeated in the
encrypted and unencrypted data of a transmission.
TABLE 3-4:
3.2.3
The status bits will always contain the output of the Low
Voltage (V
Check (CRC). If Queue (QUEN) is enabled, button
queue information will be included in the code words.
S0 S3
S0 S3
4 Bits
4 Bits
BUT
BUT
Button
LOW
FIXED CODE PORTION
STATUS INFORMATION
Overflow
Overflow
S0
S1
S2
S3
S4
S5
Counter
Counter
OVR1
2 Bits
2 Bits
OVR1
Hopping Code Portion (32 Bits)
Hopping Code Portion (32 Bits)
) detector and Cyclic Redundancy
FUNCTION CODES
Transmission Direction LSB First
OVR0
OVR0
10 Bits
10 Bits
DISC
DISC
15
15
Function Code
HCS370
Synchronization
Synchronization
DS41111D-page 11
Counter
Counter
16 Bits
xx1x
x1xx
1xxx
xxx1
11x1
16 Bits
111x
2
2
2
2
2
2
2
0
0