PCF7936AS/3851/C,1-CT NXP Semiconductors, PCF7936AS/3851/C,1-CT Datasheet - Page 23

• Manufacturer Part Number: PCF7936AS/3851/C,1-CT
• Description: pcf7936as series 32-bit 125 khz read / write security...
• Manufacturer: NXP Semiconductors

NXP Semiconductors
Security Transponder (HITAG2)
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
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.
2010 May 04
Figure 21. ASK Modulation of LF Field by the Basestation
Figure 22. Data Transmission in Write Direction
PCF7936AS
Internal Data
BPLM
Encoding
transponder demodulator circuitry has
Start of transmission
T
LOG_1
'1'
...
T
WRP
'1'
End of transmission
23
T
LOG_0
'0'
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 (T
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 (T
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 (t
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.
Last
Bit
V
Coil
LF-LOW
Condition
Stop
t
T
WAIT,Tr
STOP
V
Coil
LF-HIGH
LF field:
High
Low
LOG_0
Product Specification
respectively T
PCF7936AS
CONFIDENTIAL
WAIT,Tr
LOG_1
STOP
), see
).
) of