2.8.7.3 Demodulation Settings

RF Frequency

The ATA8510/15 supports reception in the following RF frequency bands:

• Low-Band 310 MHz to 318 MHz
• Low-Band 418 MHz to 477 MHz
• High-Band 836 MHz to 956 MHz

For each service, there are three channels that can have different RF frequency settings. All channels within one service must be configured to the same frequency band. If the channels differ by more than a certain amount, a VCO tuning process is required during the start-up of this service/channel configuration (see VCO Tuning for more information).

The RF frequency can be configured independently for each channel of each service in the eepServices.FFREQ[2:0], eepServices.FEMS and eepServices.FECT EEPROM variables (see Channel-Specific Configuration).

RF Modulation

The ATA8510/15 supports the typical modulation types ASK and FSK for short-range device applications. The ASK mode is implemented as pure on-off keying (OOK). The FSK mode allows deviations from approximately ±0.375 kHz to ±93 kHz.

The modulation type can be configured independently for path A and path B of each service in the eepServices.DMCRx.SASKx and eepServices.rxSetPathx[1].RXMODx variables.

FSK Deviation

The demodulator can handle FSK deviations from approximately ±0.375 kHz to ±93k Hz. The actual allowed range varies depending on the configured channel filter bandwidth according to parameter no. 4.40 in Electrical Characteristics. The FSK deviation can be configured independently for path A and path B of each service in the eepServices.DMCRx.DMPGx variables.

Data Rate

The demodulator can handle symbol rates from 0.5 Ksym/s to 160 Ksym/s. The actual allowed range varies depending on the configured channel filter bandwidth and modulation type according to parameters no. 4.40 and 4.60 in Electrical Characteristics. The data rate can be configured independently for path A and path B of each service in the eepServices.DMCRx.DMPGx and eepServices.DMDRx variables.

Data Coding

The demodulator supports NRZ and Manchester decoding. General hints on Manchester decoding can be found in Telegram Structure. NRZ decoding is supported for up to eight identical symbols in sequence before a signal transition must occur.

There are some rules to be respected for good NRZ reception:

• The telegram preamble shall not contain more than two consecutive high or low symbols. The best results are obtained with an alternating 0101.. symbol pattern as a preamble.
• A proper modulation amplitude threshold (see Modulation Amplitude Check) has to be selected to enable the correct operation of the DC removal feedback loop.
• The hold mode has to be activated for telegrams where more than two consecutive high or low symbols can occur. For more details, see Hold Mode.

The coding type can be configured independently for path A and path B of each service in the eepServices.DMMx.DMNEx variables.

Hold Mode

The hold mode provokes a freeze of the DC compensation if no signal transitions occur in the demodulated signal. It must be activated for NRZ coding if more than two identical consecutive symbols are possible. In Manchester mode, the hold mode must be switched off. The hold mode can be activated for path A and path B of each service independently in the eepServices.DMMx.DMHx variables.

Data Polarity

The demodulator supports both polarities for the received data. The following figure shows the demodulated data dependent on the RF signal, the data coding setting and the data polarity setting.

In NRZ mode, the demodulated data correspond to the RF signal if the data polarity is set to default; otherwise, the demodulated data are inverted. In Manchester mode, a rising edge in the middle of the bit is interpreted as ‘1’ by default.

If the data polarity is set to ‘1’, the received data are inverted before the correlation of the WUP and SFID pattern; the WUP and SFID pattern must, therefore, be symbol-wise inverted compared to the RF signal.

The data polarity setting has no influence on the raw data output on the TRPA and TRPB pins.

The data polarity can be configured independently for path A and path B of each service in the eepServices.DMMx.DMPx variables.

Data Order

The received data payload can be written byte-wise LSB-first or MSB-first to the data FIFO. The default value for the FIFO is LSB-first. The data alignment in the FIFO is visualized in the following figure, in dependency to the data order setting. Incomplete bytes are filled up with zeros.

The data order setting is implemented in the RX buffer and, therefore, has no effect on:

• WUP and SFID correlation
• Transparent data output on PC3/TMDO, PC2/TRPA or PC5/TRPB
• CRC calculation

The data order can be configured independently for path A and path B of each service in the eepServices.RXBC1.RXMSBx variables.

Raw Transparent Output

RXMode offers a raw signal output at the transparent path A (pin 16/TRPA) and transparent path B (pin 19/TRPB) pins for RXMode(transparent) and RXMode(buffered). The signal becomes visible as soon as the demodulator of the corresponding path is enabled, regardless of any signal and pattern checks. The demodulated signal is delivered unprocessed and without a corresponding clock.

The corresponding pins must be configured to output if this feature is used.

The raw transparent output can be activated independently for path A and path B of each service in the eepServices.RDOCR.ETRPx variables.