参数资料
型号: HCS473SLROM
厂商: Microchip Technology Inc.
英文描述: Code Hopping Encoder and Transponder
中文描述: 跳码编码器和转发器
文件页数: 34/68页
文件大小: 1629K
代理商: HCS473SLROM
HCS473
DS40035C-page 32
Preliminary
2002 Microchip Technology Inc.
FIGURE 3-20:
LF DATA RESPONSE ADJUSTMENTS (LFRSP=1)
FIGURE 3-21:
LF COMMUNICATION ANALOG DELAYS
3.2.7
RECEIVE STABILITY -
CALCULATING COMMUNICATION
T
E
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
DD
>
3.5V) and cold temperature. When the internal oscilla-
tor varies, both its transmitted T
E
and expected T
E
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
DD
voltages greater than
3.5V (and cold temperature) are therefore not guaran-
teed to be able to properly receive when communicated
to using an exact T
E
. When designing for these specific
operating conditions, the system designer must imple-
ment a method to adjust communication timing to the
speed of the HCS473.
Communication reliability with the transponder may be
improved by the transponder reader calculating the
HCS473’s T
E
from the Field Acknowledge sequence
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
E
calculation method
would be to time an 8T
E
sequence from the first Field
Acknowledge, then divide the value down to determine
the single T
E
value. An 8 T
E
measurement will give
good resolution and may be easily right-shifted (divide
by 2) three times for the math portion of the calculation
(Figure 3-22).
IFF, Read and Request Hop
CRC
P
H
R
(
F
(
RF Response (RFRSP=1)
Inductive
(LC Pins)
RF Response
(DATA Pin)
M
L
32-Bit LF Response (LFRSP=1)
T
FINH
1 LF
TE
Next
Command
T
CMD
T
CMD
Resulting 125 kHz on
Transponder Reader
Antenna (TX)
Digital Representation
of Communication from
Transponder Reader
600
μ
s
400
μ
s
Resulting 125 kHz on
Transponder Card
Antenna (RX)
Resulting digital signal
processed by
HCS473,
after analog filter
600
μ
s
400
μ
s
T
FILTR
T
FILTF
T
ANTR
T
ANTF
Bit ‘1’, 200
μ
s
LF
TE
Bit ‘0’, 200
μ
s
LF
TE
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