HCS412_11 Datasheet, PDF (27/52 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder and Transponder Burglar alarm systems

HCS412
4.3.8 ENABLE DEFAULT IFF COMMUNICATION
The ENABLE DEFAULT IFF COMMUNICATION com-
mand defaults certain HCS412 communication options
such that the transponder reader may communicate to
the device with a common (safe) protocol. The default
setting remains for the duration of the communication,
returning to normal only after a device RESET.
Default IFF communication settings:
• Anticollision disabled
• RF echo disabled
• 200 μs LF baud rate.
TABLE 4-9: DEFAULT IFF COMMUNICATION COMMANDS
Command
Description
Expected data In
Response
11100 Enable default IFF communication
None
None
FIGURE 4-14: ENABLE DEFAULT IFF COMMUNICATION
Activate
Field
ACK
ACK
pulses
Delay to
Command
TATO
Command
Delay
Next Command
Inductive Comms
RF Comms
Communication from reader to HCS412
Communication from HCS412 to reader
2 LFTE
Start
Command
4.4 IFF Communication Special Features
TABLE 4-10: LF COMMUNICATION
SPECIAL FEATURES (LFSP)
LFSP1:0
Description
00
No special options enabled
01
Anticollision enabled (Section 4.3.1)
10
Proximity Activation enabled
11
Anticollision and RF Echo enabled
4.4.1 PASSIVE PROXIMITY ACTIVATION
(LFSP = 10)
Enabling the Proximity Activation configuration option
allows the HCS412 to transmit a hopping code trans-
mission in response to a signal present on the LC0 pin.
FIGURE 4-15: PROXIMITY ACTIVATION
Inductive
(LF)
ACK
DATA (RF)
No command received from
reader for 255 LFTE.
LF Communication from reader to HCS412
LF Communication from HCS412 to reader
The HCS412 sends out Field Acknowledge Sequence
in response to detecting the LF field (Figure 4-1). If the
HCS412 does not receive a command before the sec-
ond field Acknowledge sequence [within 255 LFTE‘s], it
will transmit a normal code hopping transmission for 2
seconds on the DATA pin. After 2 seconds the HCS412
reverts to normal transponder mode.
The 2 second transmission does not repeat when the
device is in the presence of a continuous LF field. The
HCS412 must be RESET, remove and reapply the LF
field, to activate another transmission.
The button status used in the code hopping transmis-
sion indicates a proximity activation by clearing the S0,
S1 and S2 button activation flags.
Transmit hopping code for 2
seconds
© 2011 Microchip Technology Inc.
DS41099D-page 27