HCS200_11 Datasheet, PDF (5/34 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder 32-bit hopping code

2.0 ENCODER OPERATION
As shown in Figure 2-1, the HCS200 is a simple device
to use. It requires only the addition of buttons and RF
circuitry for use as the transmitter in your security appli-
cation. A description of each pin is described in
Table 2-1.
Note:
When VDD > 9.0V and driving low capaci-
tive loads, a resistor with a minimum value
of 50Ω should be used in line with VDD.
This prevents clamping of PWM at 9.0V in
the event of PWM overshoot.
FIGURE 2-1:
TYPICAL CIRCUITS
+12V
R (Note²)
B0
S0
VDD
B1
S1
NC
S2
PWM
Tx out
NC
Vss
2 button remote control
B3 B2 B1 B0
+12V
R (Note ²)
S0
VDD
S1
NC
S2
PWM
NC
Vss
Tx out
Note
4 button remote control (Note¹)
1: Up to 7 functions can be implemented by pressing
more than one button simultaneously or by using a
suitable diode array.
2: Resistor (R) is recommended for current limiting.
TABLE 2-1: PIN DESCRIPTIONS
Name
Pin
Number
Description
S0
S1
S2
VSS
PWM
VDD
1 Switch input 0
2 Switch input 1
3 Switch input 2/Clock pin when in
Programming mode
5 Ground reference
6 Pulse Width Modulation (PWM)
output pin/Data pin for Program-
ming mode
8 Positive supply voltage
HCS200
The HCS200 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
© 2011 Microchip Technology Inc.
DS40138D-page 5