31
August ’01
Chapter 2. Electrical Description
demodulation function.
If the Wake Pattern B (Passive Start) is detected, the circuit first checks, if the RF Amplitude
is above the threshold VWAKEB. VWAKEB is typically configured higher than VWAKEA
so that an Identification Device outside the car will not reach this RF level. It will enter the
Telegram Waiting loop (tTelegr) and then return to Standby Mode (see Figure 17).
An Identification Device inside the car will reach a higher level than VWAKEB and will
switch to Transparent Mode.
If the Wake Pattern Detection is disabled via Configuration Memory, the Transparent Mode
is entered directly from Standby Mode if VWAKEA is exceeded.
The Transparent Mode can only be left by resetting the circuit (WDEEN=low).
Figure 17: State Diagram of Transparent Mode
2.9
FSK Modulator
If enough voltage is available in the Charge Capacitor CL, the FSK Modulator of the Antenna
1 LF channel can be used by the Microcomputer (LF Transmission Mode). This is the case in
the Backup Mode (Battery Backup Mode). Instead of transmitting the response via UHF
Channel the Microcomputer activates the TX input of the TMS37122 after reaching the
Transparent Mode (see Figure 18). This causes the Continuous Pluck Circuit of the device to
activate the oscillation at Resonant Circuit 1. The resulting clock from the VCL supplied
Clock Regenerator is divided by sixteen (CLKM) and output at CLKA/M. In order to achieve
a clock synchronous operation, the modulation data must be supplied at MOD input with neg-
ative transition of the CLKM signal. Internally the MOD signal is then synchronized with the
CLKA/M positive transition before switching on or off the Modulation Capacitor (CM).
OFF
(Iquiet)
No valid or complete
WAKE PATTERN
during tWRX
WDEEN = LOW
WDEEN =
HIGH
VRF < VWAKEB
VRF > VWAKEB
Receive
Wake Pattern
for max tWRX,
Check
Wake Pattern
(Iact)
EOBI = OFF,
Wait for
tTELEGR
(Iinit)
WDEEN
= LOW
WAKE PATTERN B
received
(Passive Start)
WAKE PATTERN A
received
(Passive Entry)
VWAKEB =
ON
3DSTAT4.CH4
Wdg. = OFF
WAKE = High
EOBA = ON
CLKA = ON
(Iact)
CLKI =
OFF
tTELEGR
exceeded
CLKI
missed
for
twdg
