HCS412 Datasheet, PDF (29/44 Pages) Microchip Technology – KEELOQ Code Hopping Encoder and Transponder

HCS412
4.4.3 INTELLIGENT DAMPING (IDAMP)
FIGURE 4-19: INTELLIGENT DAMPING
A high Q-factor LC antenna circuit connected to the
HCS412 will continue to resonate after a strong LF field
is removed, slowly decaying. The slow decay makes
fast communication near the reader difficult as data bit
low times disappear.
If the Intelligent Damping option is enabled, the
HCS412 will clamp the LC pins through a 2 kΩ resistor
for 5 µs every 1/4 LFTE, whenever the HCS412 is
expecting data from the transponder reader. The intel-
ligent damping pulses start 12.5 LFTE after the
Acknowledge sequence is complete and continue for
12.5 LFTE. If the HCS412 detects data from the reader
while sending out damping pulses, it will continue to
send the damping pulses.
5 µs 1/4 LFTE 5 µs
Field
ACK
12.5 LFTE 12.5 LFTE
Bit From
reader
TABLE 4-11: INTELLIGENT DAMPING
(IDAMP)
DAMP PULSES
IDAMP
0
1
Description
Intelligent damping enabled
Intelligent damping disabled
TABLE 4-12: LF TIMING SPECIFICATIONS
Parameter
Time Element
Power-up Time
Acknowledge to Opcode Time
PPM Command Bit Time
PPM Response Bit Time
Read Response Time
IFFB = 0
IFFB = 1
Data = 0
Data = 1
Data = 0
Data = 1
IFF Response Time
Opcode to Data Input Time
Transport Code to Data Input Time
Encoder Select Acknowledge Time
IFF EEPROM Write Time (16 bits)
Op Code to Hop Code Response Time
Symbol
LFTE
TPU
TATO
TBITC
TBITR
TRT
TIT
TOTD
TTTD
TESA
TWR
TOTH
Min.
180
90
4.2
13
—
—
—
—
—
3.87
2.6
2.2
—
—
10.26
Typ.
200
100
6
4
6
2
3
13
4.3
—
—
LFTE+100
30
11.4
Max.
220
110
7.8
—
—
—
—
—
4.73
—
—
—
—
12.54
Units
µs
ms
LFTE
LFTE
LFTE
LFTE
ms
ms
ms
µs
ms
ms
© 2002 Microchip Technology Inc.
Preliminary
DS41099C-page 29