PCF7936AS/3851/C,1-CT NXP Semiconductors, PCF7936AS/3851/C,1-CT Datasheet - Page 22

• 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 Transponder Data Transmission Format
Reading from and writing to the device is accomplished by
modulating the LF field in amplitude. Since the LF field also
provides the device power supply, the modulation
characteristics have to be verified carefully, in order to
avoid a device reset due to a power low condition.
7.6.1 Read Direction
Transmission of data from the transponder to the
basestation is accomplished by absorption modulation
applied to the LF field. According to the data designated for
transmission, the transponder interface activates an
additional load that modulates the current drawn from the
transponder resonant circuit. Due to the inductive coupling
of the transponder resonant circuit and the basestation coil,
the current in the basestation coil is modulated accordingly,
resulting
modulation, see Figure 19.
In read direction the device employs either Manchester or
CDP encoding of data, see Figure 20, according to the
2010 May 04
Figure 19. LF Field Absorption Modulation
Figure 20. Data Transmission in Read Direction
in
a
Internal Data
Manchester
Encoding
CDP
Encoding
corresponding
Start of transmission
T
two-level
'1'
BIT
'1'
...
amplitude
'0'
'1'
0.5 x T
22
'0'
setting of the Immobilizer Configuration bit DCS, which is
part of the Transponder and Memory Configuration bits,
TMCF, see also section 7.1.4.
In case of Manchester encoding, a logic ‘1’ is modulated by
loading the LF field during the first half of the bit frame,
while no load is applied during the second half. A logic ‘0’ is
modulated in the opposite manner.
In case of CDP encoding, a logic ‘1’ corresponds to a state
change at the end of the bit frame. A logic ‘0’ corresponds
to a state change after the first half and at the end of the bit
frame.
In any case, the device starts with a „Load ON“ condition,
when data transmission commences.
The bit duration is a fixed multiple of the system clock
recovered from the LF field carrier.
After reception of the last bit, the basestation and control
software have to consider the indicated delay, t
before any command or data is transmitted to the device,
see also section 7.3.1.
BIT
'0'
End of transmission
V
Load ON
'1'
LF-LOW
'0'
V
Load OFF
LF-HIGH
Last
Bit
t
LF field:
Load OFF
Load ON
Load OFF
Load ON
WAIT,Bs
Product Specification
PCF7936AS
CONFIDENTIAL
WAIT,Bs
,