Microchip Technology HCS300 - Encoder Operation; Typical Circuits

© 2011 Microchip Technology Inc. DS21137G-page 5
HCS300
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
TABLE 2-1: PIN DESCRIPTIONS
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
Name
Pin
Number
Description
S0 1 Switch input 0
S1 2 Switch input 1
S2 3 Switch input 2 / Clock pin when in
Programming mode
S3 4 Switch input 3
V
SS 5 Ground reference
PWM 6 Pulse Width Modulation (PWM)
output pin / Data pin for
Programming mode
LED
7 Cathode connection for LED
V
DD 8 Positive supply voltage
VDD
B0
Tx out
S0
S1
S2
S3
LED
VDD
PWM
Vss
2 button remote control
B1
VDD
Tx out
S0
S1
S2
S3
LED
VDD
PWM
Vss
5 button remote control (Note)
B4 B3 B2 B1 B0
Note: Up to 15 functions can be implemented
by pressing more than one button
simultaneously or by using a suitable
diode array.
Power-Up
RESET and Debounce Delay
(10 ms)
Sample Inputs
Update Sync Info
Encrypt With
Load Transmit Register
Buttons
Added
?
All
Buttons
Released
?
(A button has been pressed)
Transmit
Stop
No
Yes
No
Yes
Crypt Key
Complete Code
Word Transmission