The AFEx3902-Q1 have five digital I/O pins that control I²C, SPI, PWM, and mode selection. The VREF/MODE pin must be at logic low to enable the programming interface. These devices automatically detect I²C and SPI protocols at the first successful communication after power-on, and then connect to the detected interface. After an interface protocol is connected, any change in the protocol is ignored. The I²C interface uses the A0 pin to select from among four address options. The SPI is a three-wire interface by default. No readback capability is available in three-wire SPI mode. The NC/SDO pin can be configured as the SDO function in the register map and then programmed into the NVM. With the NC/SDO pin acting as SDO, the SPI works as a four-wire interface. The SPI readback mode is slower than the write mode. The programming interface pins are:

• I²C: SCL, SDA, A0
• SPI: SCLK, SDI, SYNC, NC/SDO

All the digital pins are open drain when used as outputs. Therefore, all the output pins must be pulled up to the desired I/O voltage using external resistors.