HCS201 Datasheet, PDF (5/28 Pages) Microchip Technology – KEELOQ Code Hopping Encoder

2.0 ENCODER OPERATION
As shown in the typical application circuits (Figure 2-1),
the HCS201 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:
VDD
TYPICAL CIRCUITS
B0
S0
VDD
B1
S1
STEP
S2
DATA
VDDB
VSS
Tx out
Two button remote control
VDD
B3 B2 B1 B0
S0
S1
S2
VDDB
VDD
STEP
DATA
VSS
Four button remote control
Tx out
VDD
S0
S1
S2
VDDB
2.0-6.0V
VDD
STEP
DATA
VSS
R
Tx out
L
D
Q
C
Three button remote control with Step up regulator
External components sample values:
R = 5.1 KΩ
L = 390 uH
Q = 2N3904
C = 1.0 uF
D = ZHCS400CT (40V 0.4A Zetex)
(see Section 5.6 for a description of the Step Up circuit)
Note:
Up to 7 functions can be implemented by pressing
more than one button simultaneously or by using a
suitable diode array.
HCS201
TABLE 2-1: PIN DESCRIPTIONS
Pin Pin
Name Number
Pin Description
S0
1 Switch input 0
S1
2 Switch input 1
S2
3 Switch input 2 / Clock pin for
Programming mode
VDDB
4 Battery input pin, supplies power
to the step up control circuitry
VSS
5 Ground reference connection
DATA
6 Pulse Width Modulation (PWM)
output pin / Data pin for
Programming mode
STEP 7 Step up regulator switch control
VDD
8 Positive supply voltage
The HCS201 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.
© 2001 Microchip Technology Inc.
DS41098C-page 5