HCSXXX Datasheet, PDF (15/28 Pages) Microchip Technology – Memory Programming Specification

HCSXXX
KEELOQ devices that are capable of oscillator tuning
include the HCS201, HCS362, HCS410 and the
HCS412. Though, only the HCS201 and HCS412
transmit calibration pulses when polling the chips at the
end of write cycles.
The other two devices must be tuned according to the
preamble pulses that they transmit at the beginning of
a data packet. For the best accuracy, use multiple time
elements to achieve an average time element value.
Typically, a number that is a power of 2ⁿ is used in order
to simplify the resultant quotient (i.e., 4 or 8). In order to
obtain the most accurate time element measurement,
the widest possible baud rate should be chosen. For
simplifying the two flow diagrams below, a common
time element was chosen to the devices that share
algorithms.
The HCS362 and the HCS410 oscillator tuning register
can also be tuned as shown in the algorithm above, but
with the caveat that after the device is programmed, the
programmer must activate the target device in order to
measure the time element in the communication
preamble. A typical preamble is shown in Figure 4-3.
FIGURE 4-3:
PWM CODE WORD TRANSMISSION TIMINGS
TE TE
TE TE TE
Preamble = 23 TE
Header = 10 TE
bit 0 bit 1
 2004 Microchip Technology Inc.
Preliminary
DS41256A-page 15