Twi problem. How to read data(not include ACK)?

[aworks]

Hi.

My board : nrf51822 -Evaluation Kit ------ mma8452q

problem : read_registers(MMA8452_ADDRESS << 1,OUT_X_MSB, 6, rawData);

source code : link text

main.c -> readAccelData -> read_registers

-> twi_master_transfer(device_address | TWI_READ_BIT, value, size, TWI_ISSUE_STOP);

I can read Single Byte. I can write Single Byte.

But I can't read Multiple Byte.

MMA8452Q DataSheet MMA8452Q.pdf

Multiple Byte Read

Master:--------ACK------ACK------ACK...

Slave:ACK:Data---Data----Data---...

// MSB first
for (uint_fast8_t i = 0x80; i != 0; i>>=1)
{
    if (!twi_master_wait_while_scl_low())
    {
        transfer_succeeded = false;
        break;
    }

    if (TWI_SDA_READ())//ACK Receive
    {
        byte_read |= i;
    }
    else
    {
        // No need to do anything
    }

    TWI_SCL_LOW();
    TWI_DELAY();
}

I guess...

This code read (ACK:Data).

But can't read (Data).

How to read Data(not include ACK)?

Could you give me some tips? How to solve this problem..?

[Sebastian]

I have very similar code to yours:

bool acc_read_registers(uint8_t reg, uint8_t *data, uint8_t size)
{   bool result = false;

    // select first register to be read
    if(twi_master_transfer(TWI_MASTER_CONFIG_MMA7660_ADDRESS, &reg, 1, TWI_DONT_ISSUE_STOP))
    {
        // read bytes and finish transaction
        result = twi_master_transfer(TWI_MASTER_CONFIG_MMA7660_ADDRESS | TWI_READ_BIT, data, size, TWI_ISSUE_STOP);
    }
    
    return(result);
}

and it works correctly with both TWI versions (s/w that you are using and h/w that talks by means of TWI peripheral). I'm using SDK 7.0.1 - which one you are working with?

If you think that it could be problem in TWI driver, you may always switch to its another version - just replace file twi_sw_master.c with twi_hw_master.c and from now all timings will be controlled by h/w.

Not really sure what is exactly your problem - is there error reported during read or you are getting wrong data? The fragment of twi_sw_master.c file you have shown should read 8 bits only, just after this loop ACK or NACK is generated depending if that is last byte.

[aworks]

Thank you. But .. Where is the SDK 7.0.1 ?? I can't find SDK 7.0.1 .. How to Download SDK 7.0.1 ? My SDK version v5.1.0

[Sebastian]

SDK 7.0.1 you may find on developer site, depending on your environment you should pick PACK version (if you are using MDK 5.12 or newer) or zip. Be aware that this SDK supports natively only new boards, but you may easily adopt it to your board or just compare i2c drivers.

[aworks]

Thank you for reply.

I'm download nrf51-sdk.zip(6.1.0)

Download Site 6.1.0 : Here

SDK 6.0.1 And I'm trying to read data from the mma8452q.

But.. Same result... Read data is uncertain data...

How do i solve this problem..

[Sebastian]

You may use logic analyzer and check what is actually transmitted by MMA8452 - does it output correct data or not.