This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BOOSTXL-ADS7841-Q1: Cannot get data output from ADS7841-Q1 from TM4C1294XL

Part Number: BOOSTXL-ADS7841-Q1
Other Parts Discussed in Thread: ADS7842

Hello all,

I am working with the BOOSTXL-ADS7841-Q1 through TM4C1294's SPI interface.

I am having a problem of getting the ADC to generate output data. I checked the timing requirement and I am sure I've match everything with the datasheet.

Please take a look at my scope snippet along with the code I am using to generate the output.

Here is my setup

The Vref I am using is 4.5 V

The MISO line and the BUSY line always stay low no matter what I do

Here is the timing requirement charts for your convenience

And here is my code - I initialize the spi interface and then put the function ads7842_read_data() into an infinite loop to debug with the scope.

The CONTROL BYTE I am sending is

[1][1][0][1][0][1][1][1] = 0xD7


void init_ads7842(uint32_t sysClock) {
    uint8_t flush_buffer[10];

    /* Enable Pins for SSI usage */

    /* Enable SPI interface */

    GPIOPinTypeGPIOInput(GPIO_PORTQ_BASE, GPIO_PIN_3);  // MISO - configure it as GPIO input
    GPIOPinTypeGPIOOutput(GPIO_PORTQ_BASE, GPIO_PIN_2); // MOSI - configure it as GPIO output
    GPIOPinTypeGPIOOutput(GPIO_PORTQ_BASE, GPIO_PIN_0); // SCLK - configure it as GPIO output
    GPIOPinTypeGPIOOutput(GPIO_PORTM_BASE, GPIO_PIN_7); // ~CS - configure it as GPIO output
    GPIOPinTypeGPIOInput(GPIO_PORTP_BASE, GPIO_PIN_3);  // BUSY - configure it as GPIO input

    /* Set Chip Select To Logic High */

    /* Configure Clock, MISO and MOSI in for SSI3 */

    /* Configure the GPIO settings for the SSI pins. This function
        also gives control of these pin to the SSI hardware.*/

    /* Disable SS3 to Configure it */

    /* Configure setting for SPI interface with the speed of 8MHz - it takes 1us to send 8 bits */
    SSIConfigSetExpClk(SSI3_BASE, sysClock, SSI_FRF_MOTO_MODE_1, SSI_MODE_MASTER, 2500000, 8);

     SSI_ADV_MODE_LEGACY      0x00000000
     SSI_ADV_MODE_READ_WRITE    0x000001c0
     SSI_ADV_MODE_WRITE         0x000000c0
     SSI_ADV_MODE_BI_READ       0x00000140
     SSI_ADV_MODE_BI_WRITE      0x00000040
     SSI_ADV_MODE_QUAD_READ     0x00000180
     SSI_ADV_MODE_QUAD_WRITE    0x00000080


    /* Enable SSI3 */

    /* Flush remaning data in FIFO */
    while(SSIDataGetNonBlocking(SSI3_BASE, (uint32_t*)&flush_buffer[0]))


void ads7842_read_data() {

    uint32_t buffer[16];

    SSIDataPut(SSI3_BASE, 0xD7);
    SSIDataGet(SSI3_BASE, buffer);



void ads7842_chip_select(CHIP_SELECT option) {
    if (option == SELECT) {
        GPIOPinWrite(GPIO_PORTM_BASE, GPIO_PIN_7, 0);
        set_board_led(BOARD_LED_2, LED_ON);
    } else if (option == UNSELECT) {
        set_board_led(BOARD_LED_2, LED_OFF);

void ads7842_check_busy() {
        set_board_led(BOARD_LED_1, LED_ON);
    } else {
        set_board_led(BOARD_LED_1, LED_OFF);

Please advise me of what approach I can take to solve the issue.



  • Hello Tran,

    YOur scope shot looks good thus far. Each communication between the processor and the converter consists of eight clock cycles. But, One complete conversion is accomplished with three serial communications, for a total of 24 clock cycles on the DCLK input. Note that you will not see SDO change until the second set of 8 clock cycles after you send the control bit, all whille CS is held low. if you continue to provide clock cyles you should see SDO.

    Also, seeing how you are using a TI-boosterpack, you can also use the software available at the Boosterpack ADS7841 landing page to communicate with the device. WIth the GUI you can communiocate to the device, you can then generate scope shots showing correct communications timing schemes created by the software and use them to compare to the scope shots generated by your own software.

    Regards, Cynthia

  • Hello Cynthia,

    Thank you for the response.

    I noticed that the clock cycle only toggled when you sending in data and I assume it would toggle again when there is data coming out. As the scope showed, without data being sent in, the clock stay low. Is this perception wrong or the clock will always toggle when you pull the Chip Select low?



  • Cynthia,


    I've looked at the example GUI program and also looking at the the scope, I have a decent understanding of how the waveform should perform now.

    However, is it possible for you to get me the source code of the program on the TM4C that is written for the GUI software? it will be very helpful.



  • Hello Hau,
    I am glad that is working correctly, I also saw that your other post has also been answered, it is good to see you are moving ahead.
    Unfortunately we do not have sample software for this device. You might find sample codes for the TM4C on other community forums.