HCS300-IP Microchip Technology, HCS300-IP Datasheet - Page 7

• Manufacturer Part Number: HCS300-IP
• Description: KEE LOQ Code Hopping Encoder
• Manufacturer: Microchip Technology

again, thereby creating a permanent record of the
counter overflow. This prevents fast cycling of 64K
counter. If the decoder system is programmed to track
the overflow bits, then the effective number of unique
synchronization values can be extended to 196,608. If
programmed to zero, the system will be compatible with
the NTQ104/5/6 devices (i.e., no overflow with discrim-
ination bits set to zero).
3.6.3
If the EENC bit is set to a 1, the 32-bit fixed code part
of the transmission will also be encrypted so that it will
appear to be random. The 16-bit envelope key and
envelope algorithm will be used for encryption.
3.6.4
BSL0 and BSL1 select the speed of transmission and
the code word blanking. Table 3-3 shows how the bits
are used to select the different baud rates and
Section 5.2 provides detailed explanation in code word
blanking.
TABLE 3-3:
3.6.5
The low voltage trip point select bit is used to tell the
HCS300 what V
will be used by the device to determine when to send
the voltage low signal to the receiver. When this bit is
set to a one, the V
from a 5 volt or 6 volt V
the V
Figure 3-1 for voltage trip point.Vlow is tested at 6.3V at
-25 C and +85 C and 2.0V at -25 C and +85 C
FIGURE 3-1:
BSL1
1996 Microchip Technology Inc.
0
0
1
1
Volts (V)
DD
ENVELOPE ENCRYPTION (EENC)
LOW VOLTAGE TRIP POINT SELECT
level is assumed to be 3.0 volts. Refer to
BAUDRATE SELECT BITS (BSL0, BSL1)
BSL0
4.2
2.6
2.2
2.0
1.8
1.6
1.4
4.0
3.8
3.6
2.4
0
1
0
1
-40
DD
BAUDRATE SELECT
TYPICAL VOLTAGE TRIP
POINTS
DD
level is being used. This information
Basic Pulse
level is assumed to be operating
Element
DD
400 s
200 s
100 s
100 s
level. If the bit is set low, then
0
V
V
LOW
LOW
sel = 1
sel = 0
50
Code Words
Transmitted
1 out of 2
1 out of 2
1 out of 4
85
All
Temp (C)
V
LOW
Preliminary
4.0
4.1
The HCS300 transmission is made up of several parts
(Figure 4-1). Each transmission is begun with a
preamble and a header, followed by the encrypted and
then the fixed data. The actual data is 66 bits which
consists of 32 bits of encrypted data and 34 bits of fixed
data. Each transmission is followed by a guard period
before another transmission can begin. Refer to
Table 8-4 for transmission timing requirements. The
encrypted portion provides up to four billion changing
code combinations and includes the button status bits
(based on which buttons were activated) along with the
synchronization counter value and some discrimination
bits. The fixed portion is comprised of the status bits,
the function bits and the 28-bit serial number. The fixed
and encrypted sections combined increase the number
of combinations to 7.38 x 10
4.2
Synchronous transmission mode can be used to clock
the code word out using an external clock.
To enter synchronous transmission mode, the program-
ming mode start-up sequence must be executed as
shown in Figure 4-3. If either S1 or S0 is set on the fall-
ing edge of S2 (or S3), the device enters synchronous
transmission mode. In this mode, it functions as a nor-
mal transmitter, with the exception that the timing of the
PWM data string is controlled externally and that 16
extra bits are transmitted at the end with he code word.
The button code will be the S0, S1 value at the falling
edge S2 or S3. The timing of the PWM data string is
controlled by supplying a clock on S2 or S3 and should
not exceed 20 KHz. The code word is the same as in
PWM mode with 16 reserved bits at the end of the
word. The reserved bits can be ignored. When in syn-
chronous transmission mode S2 or S3 should not be
toggled until all internal processing has been com-
pleted as shown in Figure 4-4.
4.3
The HCS300 transmits a 66-bit code word when a but-
ton is pressed. The 66-bit word is constructed from a
Fixed Code portion and an Encrypted Code portion
(Figure 4-2).
The Encrypted Data is generated from four button bits,
two overflow counter bits, ten discrimination bits, and
the 16-bit synchronization value (Figure 8-4).
The Fixed Code Data is made up from two status bits,
four button bits, and the 28-bit serial number. The four
button bits and the 28-bit serial number may be
encrypted with the Envelope Key if the envelope
encryption is enabled by the user.
TRANSMITTED WORD
Transmission Format (PWM)
Synchronous Transmission Mode
Code Word Organization
19
.
HCS300
DS21137D-page 7