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CCS/PGA970EVM: Firmware for SPI communication

Hector Ochoa
Prodigy 160 points

Part Number: PGA970EVM

Tool/software: Code Composer Studio

We are trying to communicate to the PGA970EVM board using the SPI interface to extract data from the registers. The plan is to have the PGA970EVM take measurements from a temperature sensor, and an LVDT. The data will be extracted by a another microprocessor using SPI, and stored in a SD card. We want to PGA970 to be running a program to extract and process the data. I have already read section 7.3.1.14 of the PGA970 datasheet, and I understand the SPI protocol. I just want to know if the PGA970 already has firmware that will respond automatically to the SPI command codes? If this is true then we don't need to make any code to send the information through SPI. Also, that will explain the reason for the 24-bit SPI protocol. 

Thanks,

Hector

  • 0
    TI__Mastermind 31655 points

    Hi Hector,

    Yes, the PGA970 has built in SPI functionality, so there is no need to program special firmware to communicate with it via SPI.

    However, when the internal microcontroller is running, it locks out access to almost all of the memory space so that it is not accessible via digital interfaces (like SPI). Unfortunately the SPI interface is too slow to read the full ADC output before it updates. By the time you finish reading the lower bits of the ADC code, the upper bits may have already been updated, so when you read those they will not match with the lower bits.

    The proper way to have a digital output would be to use a custom firmware on the internal microcontroller that pulls the ADC codes (then you can process them before output) and sends them to the COMBUF registers in an interrupt service routine whenever they are called for. 

    Please see the section of the datasheet: 7.3.1.12.1 Accessing PGA970 Memories While the Microprocessor Is Running