TWI : No activity on SCL pin (27) when VDD is 1.8V

[SBharti]

Hi, 

I am using pin 27 as SCL and 26 as SDA on my custom board which is working on 1.8V. 

There is no activity on SCL pin, while i am getting correct values on SDA pin when seen on CRO.

At first i got doubt of connectivity of pins, so to test the connectivity on my board, i configured both pins as gpio and was doing PULLUP/PULLDOWN with 100millisecond delay and saw it is working. BUT it stopped working when i removed the delay, not even with 5millisec delay.

However, when i tested my firmware on "nrf52840DK" board, i saw correct waveform on both SDA/SCL lines.

Is it happening because my custom board is running on 1.8V?

Do i need to do some other configuration to use TWI at 1.8V / to use GPIO at high frequency at 1.8V?

                                                                

Running on nr552840DK board                                                                      Running on my custom board.

Regards

Suman

[SBharti]

To add more to it, I need two TWI in this design so i have used pin 27 as SCL and 26 as SDA for one TWI and pin 25 as SCL and 24 as SDA for other TWI. And i am having same issues with both SCL.

Is there any problem with these two SCL pins? Or do i need to configure them in different way.

I tried example project as well (Scanner and Sensor both). In scanner i just replaced Pin 27 as SCL and 26 as SDA. Even it is not sensing any device on bus. Also even in Sensor project, i changed SCL and SDA and address as (0xA2>>1) for EEPROM on bus, but there is no activity on SCL line, in both examples, when seen on CRO.

[Jared]

Hi,

You could try to set the SCL pin in high drive by adjusting the nrf_drv_twi.c driver accordingly:

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 */

#include "nrf_drv_twi.h"
#include <nrf_delay.h>
#include <hal/nrf_gpio.h>

#ifdef TWIM_PRESENT
#define INSTANCE_COUNT   TWIM_COUNT
#else
#define INSTANCE_COUNT   TWI_COUNT
#endif

#define SCL_PIN_INIT_CONF                                     \
    ( (GPIO_PIN_CNF_SENSE_Disabled << GPIO_PIN_CNF_SENSE_Pos) \
    | (GPIO_PIN_CNF_DRIVE_S0D1     << GPIO_PIN_CNF_DRIVE_Pos) \
    | (GPIO_PIN_CNF_PULL_Pullup    << GPIO_PIN_CNF_PULL_Pos)  \
    | (GPIO_PIN_CNF_INPUT_Connect  << GPIO_PIN_CNF_INPUT_Pos) \
    | (GPIO_PIN_CNF_DIR_Input      << GPIO_PIN_CNF_DIR_Pos))

#define SDA_PIN_INIT_CONF        SCL_PIN_INIT_CONF

#define SDA_PIN_UNINIT_CONF                                     \
    ( (GPIO_PIN_CNF_SENSE_Disabled   << GPIO_PIN_CNF_SENSE_Pos) \
    | (GPIO_PIN_CNF_DRIVE_H0H1       << GPIO_PIN_CNF_DRIVE_Pos) \
    | (GPIO_PIN_CNF_PULL_Disabled    << GPIO_PIN_CNF_PULL_Pos)  \
    | (GPIO_PIN_CNF_INPUT_Disconnect << GPIO_PIN_CNF_INPUT_Pos) \
    | (GPIO_PIN_CNF_DIR_Input        << GPIO_PIN_CNF_DIR_Pos))

#define SCL_PIN_UNINIT_CONF      SDA_PIN_UNINIT_CONF

#define SCL_PIN_INIT_CONF_CLR                                 \
    ( (GPIO_PIN_CNF_SENSE_Disabled << GPIO_PIN_CNF_SENSE_Pos) \
    | (GPIO_PIN_CNF_DRIVE_S0D1     << GPIO_PIN_CNF_DRIVE_Pos) \
    | (GPIO_PIN_CNF_PULL_Pullup    << GPIO_PIN_CNF_PULL_Pos)  \
    | (GPIO_PIN_CNF_INPUT_Connect  << GPIO_PIN_CNF_INPUT_Pos) \
    | (GPIO_PIN_CNF_DIR_Output     << GPIO_PIN_CNF_DIR_Pos))

#define SDA_PIN_INIT_CONF_CLR    SCL_PIN_INIT_CONF_CLR
//Set SCL pin in HIGH DRIVE
#define SCL_PIN_INIT_CONF_HD                                     \
    ( (GPIO_PIN_CNF_SENSE_Disabled << GPIO_PIN_CNF_SENSE_Pos) \
    | (GPIO_PIN_CNF_DRIVE_H0D1     << GPIO_PIN_CNF_DRIVE_Pos) \
    | (GPIO_PIN_CNF_PULL_Pullup    << GPIO_PIN_CNF_PULL_Pos)  \
    | (GPIO_PIN_CNF_INPUT_Connect  << GPIO_PIN_CNF_INPUT_Pos) \
    | (GPIO_PIN_CNF_DIR_Input      << GPIO_PIN_CNF_DIR_Pos))

static nrf_drv_twi_evt_handler_t m_handlers[INSTANCE_COUNT];
static void *                    m_contexts[INSTANCE_COUNT];

static void twi_clear_bus(nrf_drv_twi_config_t const * p_config)
{
    //Apply HIGH DRIVE to SCL
    NRF_GPIO->PIN_CNF[p_config->scl] = SCL_PIN_INIT_CONF_HD;
    NRF_GPIO->PIN_CNF[p_config->sda] = SDA_PIN_INIT_CONF;

    nrf_gpio_pin_set(p_config->scl);
    nrf_gpio_pin_set(p_config->sda);

    NRF_GPIO->PIN_CNF[p_config->scl] = SCL_PIN_INIT_CONF_CLR;
    NRF_GPIO->PIN_CNF[p_config->sda] = SDA_PIN_INIT_CONF_CLR;

    nrf_delay_us(4);

    for (int i = 0; i < 9; i++)
    {
        if (nrf_gpio_pin_read(p_config->sda))
        {
            if (i == 0)
            {
                return;
            }
            else
            {
                break;
            }
        }
        nrf_gpio_pin_clear(p_config->scl);
        nrf_delay_us(4);
        nrf_gpio_pin_set(p_config->scl);
        nrf_delay_us(4);
    }
    nrf_gpio_pin_clear(p_config->sda);
    nrf_delay_us(4);
    nrf_gpio_pin_set(p_config->sda);
}

#ifdef TWIM_PRESENT
static void twim_evt_handler(nrfx_twim_evt_t const * p_event,
                             void *                  p_context)
{
    uint32_t inst_idx = (uint32_t)p_context;
    nrf_drv_twi_evt_t const event =
    {
        .type = (nrf_drv_twi_evt_type_t)p_event->type,
        .xfer_desc =
        {
            .type = (nrf_drv_twi_xfer_type_t)p_event->xfer_desc.type,
            .address          = p_event->xfer_desc.address,
            .primary_length   = p_event->xfer_desc.primary_length,
            .secondary_length = p_event->xfer_desc.secondary_length,
            .p_primary_buf    = p_event->xfer_desc.p_primary_buf,
            .p_secondary_buf  = p_event->xfer_desc.p_secondary_buf,
        }
    };
    m_handlers[inst_idx](&event, m_contexts[inst_idx]);
}
#endif // TWIM_PRESENT

#ifdef TWI_PRESENT
static void twi_evt_handler(nrfx_twi_evt_t const * p_event,
                            void *                 p_context)
{
    uint32_t inst_idx = (uint32_t)p_context;
    nrf_drv_twi_evt_t const event =
    {
        .type = (nrf_drv_twi_evt_type_t)p_event->type,
        .xfer_desc =
        {
            .type = (nrf_drv_twi_xfer_type_t)p_event->xfer_desc.type,
            .address          = p_event->xfer_desc.address,
            .primary_length   = p_event->xfer_desc.primary_length,
            .secondary_length = p_event->xfer_desc.secondary_length,
            .p_primary_buf    = p_event->xfer_desc.p_primary_buf,
            .p_secondary_buf  = p_event->xfer_desc.p_secondary_buf,
        }
    };
    m_handlers[inst_idx](&event, m_contexts[inst_idx]);
}
#endif // TWI_PRESENT

ret_code_t nrf_drv_twi_init(nrf_drv_twi_t const *        p_instance,
                            nrf_drv_twi_config_t const * p_config,
                            nrf_drv_twi_evt_handler_t    event_handler,
                            void *                       p_context)
{
    uint32_t inst_idx = p_instance->inst_idx;
    m_handlers[inst_idx] = event_handler;
    m_contexts[inst_idx] = p_context;

    if(p_config->clear_bus_init)
    {
        /* Send clocks (max 9) until slave device back from stuck mode */
        twi_clear_bus(p_config);
    }

    ret_code_t result = 0;
    if (NRF_DRV_TWI_USE_TWIM)
    {
        result = nrfx_twim_init(&p_instance->u.twim,
                                (nrfx_twim_config_t const *)p_config,
                                event_handler ? twim_evt_handler : NULL,
                                (void *)inst_idx);
    }
    else if (NRF_DRV_TWI_USE_TWI)
    {
        result = nrfx_twi_init(&p_instance->u.twi,
                               (nrfx_twi_config_t const *)p_config,
                               event_handler ? twi_evt_handler : NULL,
                               (void *)inst_idx);
    }
    return result;
}

[SBharti]

Hi this didnt helped. I still cant see any activity on SCL pin.

[Jared]

Hi,

Ok, I'm not entirely sure if VDD is the issue or if it's related to the design. Do you have more samples of your custom board, are you seeing the issue on all of them? It seems that the issue is persistent even when you change the SCL, is this correct? 

Could you try to either supply your DK with 1.8 V external supply or adjust the high voltage regulator to 1.8 V by writing to the REGOUT0 register? This will make the VDD on the DK to 1.8 V. If you now flash your application on the board, what do you measure on SCL?

Could you share the schematics? I can make the case private if you prefer it. Are you using any external pulldowns/pullups?

regards

Jared

[SBharti]

Hi Jared,

To test whether it is hardware or software issue, i configured these pins 0.26 and 0.27 as GPIO and make it HIGH/LOW with interval.

My observations on CRO:

Pin 0.26 is working fine, but found issue at Pin 0.27.

At low frequency both pins are working fine with correct HIGH/LOW transition, but with increasing frequency, at pin 0.27, its transition is not steep. When it is going HIGH, its not moving directly from LOW to HIGH but going with curve. With increasing frequency this effect increases.

What may cause this issue?

[Jared]

Hi,

This is regarding your custom board right? Not the development kit?

What frequency are you observing this at? Could you share a trace of it?

regards

Jared