The AFE4400 is a pulse oximetry analog front-end chip by TI. It controls LED switching, has ambient light cancellation, and other very nice features for pulse oximetry applications.
The main communication interface for the AFE4400 is via SPI. However, there are also some digital pins that can be configured for smoother operation; two are required and four are for additional diagnostic value.
adc_pdn: The powerdown pin; should be held high (not floating!) for the duration of operation.
adc_rdy: The "ADC Ready" pin, indicating a sample is ready for reading. It is useful to use
adc_rdyas the driver for an edge-triggered interrupt.
daig_end: Diagnostics complete
adc_done: ADC conversion complete
led_err: Connection issue with the LEDs
sensor_err: Connection issue with the photodiodes
Controller in charge of communication with AFE4400
Possible AFE4400 errors.