HCS360_01 Datasheet, PDF (4/28 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder

HCS360
2.0 DEVICE OPERATION
As shown in the typical application circuits (Figure 2-1),
the HCS360 is a simple device to use. It requires only
the addition of buttons and RF circuitry for use as the
transmitter in your security application. A description of
each pin is described in Table 2-1.
FIGURE 2-1: TYPICAL CIRCUITS
VDD
B0
S0
VDD
B1
S1
LED
S2
PWM
S3
VSS
2 button remote control
B4 B3 B2 B1 B0
VDD
Tx out
S0
VDD
S1
LED
S2
PWM
S3
VSS
Tx out
5 button remote control (Note)
Note: Up to 15 functions can be implemented by
pressing more than one button simulta-
neously or by using a suitable diode array.
TABLE 2-1: PIN DESCRIPTIONS
Name
Pin
Number
Description
S0
S1
S2
S3
VSS
PWM
LED
VDD
1 Switch input 0
2 Switch input 1
3 Switch input 2/Can also be clock
pin when in programming mode
4 Switch input 3/Clock pin when in
programming mode
5 Ground reference connection
6 Pulse width modulation (PWM)
output pin/Data pin for
programming mode
7 Cathode connection for directly
driving LED during transmission
8 Positive supply voltage
connection
The high security level of the HCS360 is based on the
patented KEELOQ technology. A block cipher type of
encryption algorithm based on a block length of 32 bits
and a key length of 64 bits is used. The algorithm
obscures the information in such a way that even if the
transmission information (before coding) differs by only
one bit from the information in the previous transmis-
sion, the next coded transmission will be totally differ-
ent. Statistically, if only one bit in the 32-bit string of
information changes, approximately 50 percent of the
coded transmission will change. The HCS360 will wake
up upon detecting a switch closure and then delay
approximately 6.5 ms for switch debounce (Figure 2-
2). The synchronization information, fixed information,
and switch information will be encrypted to form the
hopping code. The encrypted or hopping code portion
of the transmission will change every time a button is
pressed, even if the same button is pushed again.
Keeping a button pressed for a long time will result in
the same code word being transmitted until the button
is released or time-out occurs. A code that has been
transmitted will not occur again for more than 64K
transmissions. This will provide more than 18 years of
typical use before a code is repeated based on 10
operations per day. Overflow information programmed
into the encoder can be used by the decoder to extend
the number of unique transmissions to more than
128K.
If, in the transmit process, it is detected that a new but-
ton(s) has been pressed, a reset will immediately be
forced and the code word will not be completed. Please
note that buttons removed will not have any effect on
the code word unless no buttons remain pressed in
which case the current code word will be completed
and the power down will occur.
DS40152D-page 4
 2001 Microchip Technology Inc.