Reliable and Expandable SPI Interface for Multichannel ADC

Reliability and built in test are very important parameters for the development of product. Reliability ensures the consistent working of product without failure for long term. Built In Test Equipment (BITE) ensures the ability of the product to test itself. This paper presents the implementation of SPI interface to work with multichannel ADC and also illustrates how the reliability and BITE are achieved. Analog to digital converters are mainly used in embedded systems to convert the analog data received by the sensors to digital data. ADCs only provide the real time connectivity to the digital world. Recent trends in semiconductor technology incorporate the multiple numbers of ADCs, and DACs into controllers, and FPGAs. Controllers with inbuilt ADCs and DACs are considered mainly for static applications, whereas FPGAs such as RFSoCs from M/s Xilinx and M/s Intel are used for dynamic applications mainly for high frequency RF bands where stringent task of synchronization across the channels has been simplified. STM32F7 has 19 ADCs as on-chip peripherals. But, if more number of ADC channels are required, or if requirement of other peripherals such as UART, I2C, Ethernet, GPIOs etc is increased, or even few of the inbuilt ADCs cannot be used due to shortage of the dedicated pins, then external ADC is to be used. STM32F7 series controllers are equipped with a Serial peripheral Interconnect (SPI) bus, I2C, UART, etc to communicate with the off chip peripherals. ADC ICs are available with data transfer interfaces such as SPI, I2C, UART etc. This claim presents the hardware interfacing of ADC with SPI interface to STM32F7 Microcontroller and the unique implementation using SPI interface. Microcontroller facilitates an easy unique implementation of 3-wire SPI serial interface. Slave select line is hardwired to save a pin if there are no multiple slave devices connected. A methodology is presented to expand the interconnections of more numbers of ADCs with limited GPIOs.