PCF7936AS View Datasheet(PDF) - NXP Semiconductors.
Part Name
Description
MFG CO.
'PCF7936AS' PDF : 33 Pages View PDF
NXP Semiconductors
Security Transponder (HITAG2)
Product Specification
PCF7936AS
7.6.2 Write Direction
Transmission of data from the basestation to the
transponder is accomplished by Amplitude Shift Keying
(ASK) of the LF field with a modulation index as specified.
According to the data designated for transmission, the
basestation coil driver is simply switched ON and OFF (tri-
state) typically. Due to the inductive coupling of the
transponder resonant circuit and the basestation coil, the
voltage of the transponder resonant circuit is modulated
accordingly. Resulting in a two-level amplitude modulation
that is detected by the transponder interface demodulator
circuitry, see Figure 21.
The PCF7936AS transponder demodulator circuitry has
been optimized for basestations with antenna coil drivers
that perform the LF field modulation by Tri-State switching
of the driver stage.
In write direction Binary Pulse Length Modulation (BPLM) is
applied for data encoding, see Figure 22.
Sending data or commands to the device commences with
an initial write pulse that marks transmission start. A logic
‘0’ or ‘1’ is signaled to the transponder by the
corresponding repetition time (TLOG_0 respectively TLOG_1) of
the write pulse sequence.
The end of the transmitted bit string is marked by a stop
condition. A stop condition is detected by the transponder,
if no write pulse is detected for the specified time (TSTOP).
In the case the bit string transmitted causes the device to
respond with data, modulation of the LF field by the device
does commence after the specified time out (tWAIT,Tr), see
also section 7.3.1.
Violation of the specified timing causes an error condition,
upon which the device enters the WAIT state, see also
section 7.2.
Figure 21. ASK Modulation of LF Field by the Basestation
VLF-LOW
Coil
VLF-HIGH
Coil
Start of transmission
Internal Data
BPLM
Encoding
'1'
...
End of transmission
tWAIT,Tr
'1'
'0' Last
Stop
Bit Condition
TLOG_1
TWRP
TLOG_0
Figure 22. Data Transmission in Write Direction
TSTOP
LF field:
High
Low
2010 May 04
23
CONFIDENTIAL
Share Link: 
