HCS473 Datasheet, PDF (26/68 Pages) Microchip Technology – Code Hopping Encoder and Transponder

HCS473
3.2.3.1 SELECT TRANSPONDER
The SELECT TRANSPONDER sequence must imme-
diately follow the HCS473 wake-up. A 12-bit Vehicle ID
(VID) follows the 3-bit command. The 4-bit Token ID
(TID) is sent by pulsing the field to identify which tran-
sponder should respond.
The HCS473 counts each time the field is pulsed (6
LFTE period), the first pulse setting the counter equal to
0. If the VID matched, the HCS473 will send an
Acknowledge when the TID matches the counter. Any
further TID pulses after the Acknowledge occurs will
deselect the device, putting it back to SLEEP - again
requires a wake-up sequence to communicate.
Any HCS473 that did not match both the presented VID
and TID will return to SLEEP, unselected, remaining
that way until the next wake-up pulse occurs.
The next command must begin TTSCMD after the
Acknowledge. If the LC input is high a point TTSCMD_MIN
after the Acknowledge ends, the HCS473 will return to
SLEEP, unselected, assuming the transponder reader
is sending additional TID pulse(s) to select a different
device. A device of any TID value may therefore be
uniquely selected, regardless if a device with lower TID
has already acknowledged.
FIGURE 3-12:
TRANSPONDER SELECT SEQUENCE (RF RESPONSE EXAMPLE)
WAKE ACK
TCMD
‘000₂’
12 bits
1-16
Pulses
‘XXX’
TTSCMD
CMD VID TID ACK
CMD
Command
12-Bit
VID
TID=0 TID=1 TID=2 TID=3
Next
Command
TSF
Inductive In
(LC Pins)
RF Response
(DATA Pin)
TCMD
ACK
TCMD
6 LFTE
5 LFTE
TTSACK
TTSCMD
Transponder Select ACK
Example for TID=’0011’
16-bit Device Identifier
DID
= [ 12-bit Vehicle ID ] [ 4-bit Token ID ]
VID
TID
DS40035C-page 24
Preliminary
 2002 Microchip Technology Inc.