8.3.4 FOUNDATION Fieldbus or PROFIBUS PA Manchester Decoder

The FOUNDATION Fieldbus and PROFIBUS PA decoder converts the Manchester encoded data applied at the MOD_IN or MOD_INF pins, depending on whether an external filter is implemented, to binary data that is loaded into a receive FIFO. Data in the receive FIFO can then be read by the host controller via UART or SPI serial interfaces.

When valid data is provided to the decoder, binary data is read out serially on the UART interface. For SPI devices, the receive FIFO is loaded until the threshold programmed in FIFO LEVEL SET is met which will trigger an interrupt on the IRQ pin. The MODEM STATUS register can then be read to determine the source of the interrupt, which includes a bit for the FIFO level in DB7, indicating that data is ready to be read on the SPI bus. More details are explained in the respective Device Functional Modes sections.