HTRM800 Ver la hoja de datos (PDF) - Philips Electronics
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HTRM800 Datasheet PDF : 20 Pages
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Philips Semiconductors
HITAG long range reader module
hardware
Product specification
HTRM800 family
7.3.2 INTERFACE MICROCONTROLLER TO HOST
The device communicates with the host system via a serial
interface using a baud rate of 9600 baud. Data transfer
details are: 1 start bit, 8 data bits, 1 stop bit, no parity bit
and the least significant bit is sent first.
Version HTRM800/AED has an integrated RS232 level
driver. Version HTRM800/CED is wired with an RS485
level driver and version HTRM800/EED is wired with a
CMOS level driver.
7.3.3 TRANSMITTING PART
For transmitting power and data to the transponder a
125 kHz sine signal is switched by the microcontroller and
amplified. The amplifier is designed as a current source.
A voltage limiter is used to clamp the output voltage of the
amplifier during the decay and transient phases of the sine
signal.
7.3.4 RECEIVING PART
After filtering and demodulation of the amplitude
modulated signal received from the transponder, the
received data is converted and passed to the Digital Signal
Processing (DSP) unit for further processing.
7.3.5 DIGITAL SIGNAL PROCESSING UNIT
The receiving part of the reader module includes
bandpass filters which attenuate disturbances (3 dB
attenuation at 105 and 145 kHz). For disturber
frequencies near the 125 kHz (e.g. harmonics of the line
frequency of PC monitors, long wave transmitters) a
fourier transformation is used to recognize harmonic
disturbers and to eliminate their influence. The DSP is also
responsible for separating the responses of different
transponders during anticollison cycles (multiple
transponder operation).
7.3.6 PERIODIC DISTURBERS
There are a couple of possible sources for disturbances for
a 125 kHz system like HITAG. The HTRM800 is designed
to handle this problem and achieve optimal performance
under worst conditions.
Long wave transmitters, other 125 kHz systems and
PC monitors are examples for periodic disturbers which
can be relevant for 125 kHz systems. To eliminate these
disturbers the digital signal processing unit is used.
After the command StartFFT is sent to the reader module
a Fast Fourier Transformation (FFT) is started to locate
periodic disturbers. After about 110 ms this calculation is
finished and for the following communication between
reader module and transponder the located disturbers are
eliminated. The command StartFFT should be executed
as often as the application allows.
Remarks:
1. The DSP is able to suppress up to two harmonic
electromagnetic disturbances
2. During FFT is running (about 110 ms) communication
with a transponder is not possible.
7.3.7 VOLTAGE REGULATING UNIT
The reader module contains some filtering circuits which
supply all parts of the reader module with the required
voltages. Nevertheless some requirements are to be
fulfilled by the external power supply. This means the
maximum ripple of the supply voltages must not exceed
the values specified in Chapter 8.
7.3.8 STANDBY MODE
The HTRM800 offers a software controlled standby mode.
This mode can be activated and deactivated by the host
system. During the standby mode the amplifier is turned off
and the power consumption decreases drastically.
7.3.9 BEHAVIOUR WITH HITAG 1 TRANSPONDERS
If several HITAG 1 transponders arrive simultaneously
within the communication field of the antenna of a
HTRM800, all the transponders (theoretically up to 232)
within the communication field of the antenna can be read
and written simultaneously. Because of the mutual
influence of the transponder coils - they detune each other
if there are too many too close to each other - the number
of the transponders that can be operated simultaneously is
limited.
7.3.10 BEHAVIOUR WITH HITAG 2 TRANSPONDERS
If several HITAG 2 transponders arrive simultaneously
within the communication field of the antenna of a
HTRM800, the ‘stronger’ transponder (the nearer one)
takes over or - under special circumstances - no
communication takes place. If the transponders arrive in
the field one after the other, communication is established
with the first one, all the other transponders are ignored.
This ensures that no two (or several) HITAG 2
transponders will ever be processed (above all written to!)
accidentally at the same time. By muting a selected
HITAG 2 transponder (HALT mode) another HITAG 2
transponder that is to be found in the communication field
of the antenna can be recognized.
2001 Oct 04
7
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