3.5.2.1 Modulation Data Source

There are three different TX data sources available that can be configured in the FSCR.TXMS register:

• Buffered mode: TX modulator output SO4TX

  Two hardware FIFOs (DFIFO and SFIFO) are available that can hold transmission data. The data is read directly by the TX modulator block that has additional data manipulation features to build a complete telegram. Then, the data is serialized on the SO4TX line and can be used as input for the TX DSP if FSCR.TXMS = 0b1x. The complete function is already implemented in firmware as TXMode(buffered) (see TXMode (buffered)).

• Register controlled: Manual TX modulation via register bit

  The modulation signal can be controlled by the single register bit FSCR.TXMOD. This bit is accessible by the AVR, and, therefore, can also be written by a “Write SRAM/Registers” SPI command. The current value of this bit is used directly as a modulation source if FSCR.TXMS = 0b00. There is no firmware function available that is associated with this modulation source.

• Transparent mode: Pin-controlled data input via pin 18 (TMDI)

  If FSCR.TXMS = 0b01, the TMDI input pin 18 is used as a transparent modulation data source. The data signal has to be provided with the correct data rate and coding (Manchester, NRZ, …). The firmware function TXMode(transparent) is available to activate this mode (see TXMode (transparent)).