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HTRM800 Datasheet(PDF) 7 Page - NXP Semiconductors |
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HTRM800 Datasheet(HTML) 7 Page - NXP Semiconductors |
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7 / 20 page  2001 Oct 04 7 Philips Semiconductors Product specification HITAG long range reader module hardware 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. |
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Similar Description - HTRM800 |
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