HCS410 Datasheet, PDF (8/36 Pages) Microchip Technology – KEELOQ CODE HOPPING ENCODER AND TRANSPONDER

HCS410
2.2 Code Hopping Mode (CH Mode)
The HCS410 wakes up upon detecting a switch closure
and then delays approximately 30 ms for switch
debounce (Figure 2-7). The synchronization counter
value, fixed information, and switch information are
encrypted to form the code hopping portion. The
encrypted or code hopping portion of the transmission
changes every time a button is pressed, even if the
same button is pushed again. Keeping a button
pressed for a long time results in the same code word
being transmitted until the button is released or time-
out occurs. A code that has been transmitted will not
occur again for more than 64K transmissions. Overflow
information programmed into the encoder can be used
by the decoder to extend the number of unique trans-
missions to more than 192k.
If, during the transmit process, it is detected that a new
button(s) has been added, a reset will immediately be
forced and the 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 current code word will be completed
and the power down will occur. If, after a button combi-
nation is pressed, and the same button combination is
pressed again within 2 seconds of the first press, the
current transmission will be aborted and a new trans-
mission will start with the queue counter (QUE)
incremented.
FIGURE 2-7: CODE HOPPING ENCODER OPERATION
Power-up
(A button has been
pressed (Note1)
Sample Inputs
Update Sync Info
Complete current
code word while
checking buttons
(Note 2)
No _Transmitted Yes
7 complete code
Stop transmitting
words?
immediately
Encrypt With
Encoder Key
Transmit
20-second Yes
timeout
No
Buttons added?
Yes
No
All buttons
No
released?
(Note 1)
Yes
DINC
Set?
No
Yes
No
Buttons
pressed?
(Note 1)
No
20 second
time-out
completed?
Yes
Yes
2 second
time-out
completed?
Yes
Yes
DINC Set?
No
Increase sync
counter
by 12
Power down
No
No
Buttons
pressed?
(Note 1)
Yes
No
Same as
previous
press?
Yes
Increment queue
counter
Note 1: 30 ms debounce on press and release of all buttons.
2: Completes a minimum of 3 code words if MTX3 is set.
DS40158C-page 8
Preliminary
© 1997 Microchip Technology Inc.