1999 Microchip Technology Inc.
Preliminary
DS21137E-page 5
HCS300
2.0
DEVICE OPERATION
As shown in the typical application circuits (Figure 2-1),
the HCS300 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
TABLE 2-1:
PIN DESCRIPTIONS
The high security level of the HCS300 is based on the
patented
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 transmission, the next
coded transmission will be totally different. Statistically,
if only one bit in the 32-bit string of information
changes, approximately 50 percent of the coded trans-
mission will change. The HCS300 will wake up upon
detecting a switch closure and then delay approxi-
mately 10 ms for switch debounce (Figure 2-2). The
synchronized information, fixed information, and switch
information will be encrypted to form the hopping code.
The encrypted or hopping code portion of the transmis-
sion 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
timeout 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 192K.
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.
V
DD
B0
Tx out
S0
S1
S2
S3
LED
V
DD
PWM
V
SS
2 button remote control
B1
V
DD
Tx out
S0
S1
S2
S3
LED
V
DD
PWM
V
SS
5 button remote control (Note)
B4 B3 B2 B1 B0
Note:
Up to 15 functions can be implemented by press-
ing more than one button simultaneously or by
using a suitable diode array.
Name
Pin
Number
Description
S0
1
Switch input 0
S1
2
Switch input 1
S2
3
Switch input 2/Can also be clock
pin when in programming mode
S3
4
Switch input 3/Clock pin when in
programming mode
V
SS
5
Ground reference connection
PWM
6
Pulse width modulation (PWM)
output pin/Data pin for
programming mode
LED
7
Cathode connection for directly
driving LED during transmission
V
DD
8
Positive supply voltage
connection
21137e.Book Page 5 Monday, October 4, 1999 8:04 AM
