HCS410 Datasheet, PDF (18/36 Pages) Microchip Technology – KEELOQ CODE HOPPING ENCODER AND TRANSPONDER

HCS410
2.6 IFF Special Features
2.6.1 ANTI-COLLISION (ACOLI)
When the ACOLI bit is set in the configuration word,
anti-collision mode is entered. The HCS410 will start
sending ACK pulses when it enters a magnetic field.
The ACK pulses stop as soon as the HCS410 detects
a start bit from the decoder. A ‘select encoder’ opcode
(00000) is then sent out by the decoder, followed by a
32-bit serial number. If the serial number matches the
HCS410’s serial number, the HCS410 will acknowl-
edge with the acknowledge sequence as shown in
Figure 2-19. The HCS410 can then be addressed as
normal. If the serial number does not match, the IFF
encoder will stop transmitting ACK pulses until it is
either removed from the field or the correct serial num-
ber is given.
FIGURE 2-19: SERIAL NUMBER CORRECT
ACKNOWLEDGE SEQUENCE
TE
LC0/1
3 TE
TE
2.6.2 TRANSPONDER IN/RF OUT
When in transponder mode with ACOLI and XPRF set,
the outputs of the HCS410’s LC0:LC1 pins are echoed
on the PWM output line. After transmitting the data on
the LC pins, the data is then transmitted on the PWM
line. The transmission format mirrors a code hopping
transmission. The response replaces the 32-bit code
hopping portion of the transmission. If the response is
a 16-bit response, the 16 bits are duplicated to make up
the 32-bit code hopping portion. The preamble, serial
number, CRC, and queuing bits are all transmitted as
normal (Figure 2-18).
This feature will be used in applications which use RF
for long distance unidirectional authentication and
short distance IFF.
2.6.3 INTELLIGENT DAMPING
If the LC circuit on the transponder has a high Q-factor,
the circuit will keep on resonating for a long time after
the field has been shut down by the decoder. This
makes fast communication from the decoder to the
HCS410 difficult. If the IDAMP bit is set to 0, the
HCS410 will clamp the LC pins for 5 µs every 1/4 TE,
whenever the HCS410 is expecting data from the
decoder. Refer to Figure 2-18 for timing details. This
option can be set in the configuration word.
2.7 LED Indicator
If a signal is detected on LC0, the LED pin goes high for
30 ms every 8s (IFFB = 0) or 4s (IFFB 1) to indicate that
the power source is charging.
FIGURE 2-20: LED INDICATOR WHEN CHARGING POWER SOURCE
LC0
LED
IFFB = 0
LED
IFFB = 1
4s
2s
4s
8s
30 ms
30 ms
DS40158C-page 18
Preliminary
© 1997 Microchip Technology Inc.