hcs473 Microchip Technology Inc., hcs473 Datasheet - Page 34

• Manufacturer Part Number: hcs473
• Description: Code Hopping Encoder And Transponder
• Manufacturer: Microchip Technology Inc.

HCS473
FIGURE 3-20:
FIGURE 3-21:
3.2.7
The HCS473’s internal oscillator may vary ±10% over
the device’s rated voltage and temperature range for
commercial temperature devices. A certain percentage
of industrial temperature devices vary further on the
slow side, -20%, when used at higher voltages (V
3.5V) and cold temperature. When the internal oscilla-
tor varies, both its transmitted T
when receiving will vary.
The HCS473 receive capability is ensured over a ±10%
oscillator variance, with receive capability no longer
robust as oscillator variance approaches ±15%. Indus-
trial devices operating at V
3.5V (and cold temperature) are therefore not guaran-
teed to be able to properly receive when communicated
to using an exact T
operating conditions, the system designer must imple-
ment a method to adjust communication timing to the
speed of the HCS473.
DS40035C-page 32
IFF, Read and Request Hop
RF Response
(LC Pins)
(DATA Pin)
Inductive
RECEIVE STABILITY -
CALCULATING COMMUNICATION
T
E
of Communication from
Digital Representation
processed by HCS473,
Resulting digital signal
Transponder Reader
Resulting 125 kHz on
Resulting 125 kHz on
Transponder Reader
Transponder Card
after analog filter
Antenna (RX)
Antenna (TX)
E
. When designing for these specific
LF DATA RESPONSE ADJUSTMENTS (LFRSP=1)
LF COMMUNICATION ANALOG DELAYS
CRC
DD
voltages greater than
E
and expected T
T
ANTR
T
FILTR
RF Response (RFRSP=1)
Bit ‘1’, 200 µs LF
DD
Preliminary
600 µs
>
E
600 µs
T
FILTF
TE
Communication reliability with the transponder may be
improved by the transponder reader calculating the
HCS473’s T
and using this exact time element in communication to
and in reception routines from the transponder.
Always begin and end the time measurement on rising
edges. Whether LF or RF, the falling edge decay rates
may vary but the rising edge relationships should
remain consistent. A common T
would be to time an 8T
Acknowledge, then divide the value down to determine
the single T
good resolution and may be easily right-shifted (divide
by 2) three times for the math portion of the calculation
(Figure 3-22).
T
ANTF
32-Bit LF Response (LFRSP=1)
1 LF
E
E
Bit ‘0’, 200 µs LF
TE
from the Field Acknowledge sequence
value. An 8 T
400 µs
400 µs
T
FINH
E
 2002 Microchip Technology Inc.
sequence from the first Field
TE
E
T
measurement will give
CMD
E
calculation method
Command
Next
T
CMD