HCS362-I Datasheet, PDF (8/38 Pages) Microchip Technology – KEELOQ Code Hopping Encoder

HCS362
3.0 DEVICE OPERATION
The HCS362 will wake-up upon detecting a switch clo-
sure and then delay for switch debounce (Figure 3-1).
The synchronization information, fixed information and
switch information will be encrypted to form the hop-
ping code. The encrypted or hopping code portion of
the transmission 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 time-out occurs.
The time-out time can be selected with the Time-out
(TIMOUT[0..1]) configuration option. This option
allows the time-out to be disabled or set to 0.8 s, 3.2 s
or 25.6 s. When a time-out occurs, the device will go
into SLEEP mode to protect the battery from draining
when a button gets stuck.
If in the transmit process, it is detected that a new but-
ton is pressed, the current code word will be aborted. A
new code word will be transmitted and the time-out
counter will RESET. If all the buttons are released, the
minimum code words will be completed. The minimum
code words can be set to 1,2,4 or 8 using the Minimum
Code Words (MTX[0..1]) configuration option. If the
time for transmitting the minimum code words is longer
than the time-out time, the device will not complete the
minimum code words.
Note:
Buttons removed will not have any
effect on the code word unless no but-
tons remain pressed in which case the
current code word will be completed
and the power-down will occur.
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 trans-
missions to more than 192K.
FIGURE 3-1: BASIC FLOW DIAGRAM OF
THE DEVICE OPERATION
START
Sample Buttons
Get Config.
Seed
Yes
TX?
No
Increment
Counter
Read
Seed
Encrypt
Transmit
Yes
Time-out
No
No
MTX
STOP
Yes
No
Buttons
Yes
No
Seed ^Yes Seed
Yes
Time
Button
No
No
No
New
Buttons
Yes
DS40189D-page 8
Preliminary
© 2002 Microchip Technology Inc.