HCSXXX Datasheet, PDF (12/28 Pages) Microchip Technology – Memory Programming Specification

HCSXXX
2.8 Verify Mode
In terms of verify operations, all KEELOQ encoders and
transponders incorporate a security feature that only
allows one verify operation to be completed, and it
must be completed at the end of the programming
sequence before exiting the Programming mode.
When implementing polling routines to sense the end
of the last write cycle and after driving the clock line low,
the programmer can begin to read data by continuing
to provide clock cycles to the target device. Note that
there is not an Acknowledge bit from KEELOQ devices
during the Verify mode.
In the case where the programmer provides a time delay
to allow for write cycle completion, the programmer can
provide clock cycles after the delay to begin reading
data.
Note: Decoders do not incorporate a verify
function.
3.0 CONFIGURATION WORD
For detailed descriptions of bit functions for the
configuration words of the KEELOQ devices, be sure to
download the latest Data Sheet for the respective device
from the Microchip Technology web site
(www.microchip.com). Configuration word architectures
are also shown earlier in Section 2.0 “Memory
Mapping”.
4.0 OSCILLATOR TUNING
Calibrating the oscillator of select devices can be
completed a number of ways. For the purpose of this
document, calibration will be completed using the Two-
Point Calibration Algorithm, which is described in
Application Note AN824, “KEELOQ® Encoders
Oscillator Calibration” (DS00824). The algorithm is as
follows:
• OSCCAL = -8
• Program target device
• Measure oscillator frequency FHIGH
• OSCCAL = +7
• Program target device
• Measure oscillator frequency FLOW
• Interpolate:
- OSCCAL = 16*(FIDEAL - FLOW)/(FHIGH - FLOW)
• Program target device
For a better understanding of how to implement this
algorithm, the following flow charts are being provided:
DS41256A-page 12
Preliminary
 2004 Microchip Technology Inc.