HCS300_01 Datasheet, PDF (5/28 Pages) Microchip Technology – KEE LOQ Code Hopping Encoder

2.0 ENCODER 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 given in Table 2-1.
FIGURE 2-1:
TYPICAL CIRCUITS
VDD
B0
S0
VDD
B1
S1
LED
S2
PWM
S3
Vss
Tx out
2 button remote control
VDD
B4 B3 B2 B1 B0
S0
VDD
S1
LED
S2
PWM
S3
Vss
Tx out
Note:
5 button remote control (Note)
Up to 15 functions can be implemented
by pressing more than one button
simultaneously 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 / Clock pin when in
Programming mode
4 Switch input 3
5 Ground reference
6 Pulse Width Modulation (PWM)
output pin / Data pin for
Programming mode
7 Cathode connection for LED
8 Positive supply voltage
HCS300
The HCS300 will wake-up upon detecting a button
press and delay approximately 10 ms for button
debounce (Figure 2-2). The synchronization counter,
discrimination value and button information will be
encrypted to form the hopping code. The hopping code
portion will change every transmission, even if the
same button is pushed again. A code word that has
been transmitted will not repeat for more than 64K
transmissions. This provides more than 18 years of use
before a code is repeated; based on 10 operations per
day. Overflow information sent from the encoder can be
used 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
occur and the current 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 code word will be completed
and the power-down will occur.
FIGURE 2-2:
ENCODER OPERATION
Power-Up
(A button has been pressed)
RESET and Debounce Delay
(10 ms)
Sample Inputs
Update Sync Info
Encrypt With
Crypt Key
Load Transmit Register
Transmit
Yes
Buttons
Added
?
No
All
No
Buttons
Released
?
Yes
Complete Code
Word Transmission
Stop
© 2001 Microchip Technology Inc.
DS21137F-page 5