JAJSNU3 December 2023 AFE782H1 , AFE882H1
PRODUCTION DATA
The HART demodulator converts the HART FSK input signals applied at the HART input pins (RX_IN and RX_INF) to binary data that are enqueued into the receive FIFO (FIFO_H2U). Data from the FIFO_H2U can then be dequeued by the host controller using the SPI or output on UARTOUT. Figure 6-23 shows the HART demodulator architecture. The AFEx82H1 supports two different input bandpass filter modes: internal and external.
In internal filter mode, the HART input signal is connected to the RX_IN pin through the high-pass filter capacitor. In this mode, the low-pass filter capacitor is connected to the RX_INF pin.
In external filter mode, the band-pass filter is implemented with external components for better flexibility, and the resulting band-pass-filtered signal is connected to the RX_INF pin. In this mode, float the RX_IN pin.
Use the MODEM_CFG.RX_EXFILT_EN bit to select between these two modes, depending on the external band-pass filter implementation and HART input signal connection.
The input band-pass filter (either fully external or partially internal with external capacitors and internal resistors) is followed by the internal second-order high-pass filter and the internal second-order low-pass filter. To enable the second-order low-pass filter, use the MODEM_CFG.RX_HORD_EN bit.
The HART demodulator asserts a carrier detect (CD) signal, when a carrier-above-threshold level is detected. Hysteresis is implemented with the carrier-detect feature to prevent erroneous carrier-detection signals. The glitch-free CD signal is available internally to the arbiter and externally to the system controller on the CD pin.