Switch SPI Clock Polarity Before Receive

[taboteke]

I am interfacing nrf52832 with TI TRF7960A using SDK 14.2.0

According to Application Report (http://www.ti.com/lit/an/sloa140a/sloa140a.pdf) ,

when receive data, SPI mode must change from mode-1 to mode-0.

This is how MSP430 do

SPI_sendByte(*pui8Buffer);

#if (TRF79xxA_VERSION == 60)
	UCB0CTL1 |= UCSWRST;
	UCB0CTL0 &= ~UCCKPH;					// Switch Clock Polarity for Read (TRF7960A)
	UCB0CTL1 &= ~UCSWRST;
#endif

	while(ui8Length-- > 0)
	{
		*pui8Buffer = SPI_receiveByte();
		pui8Buffer++;
	}
	while(UCB0STAT & UCBUSY)
	{
	}

#if (TRF79xxA_VERSION == 60)
	UCB0CTL0 |= UCCKPH;						// Switch Clock Polarity back
#endif
	SLAVE_SELECT_HIGH; 						// Stop SPI Mode

Is there a function in SPI Master driver that able to switch polarity before read?

Many thanks for the assistance.

Regards,

Leo

[Håkon Alseth]

Hi Leo,

 

We do not have an automated functionality to switch modes on-the-fly in hardware, but: You can send a SPIM command with SPI MODE 0, then configure the SPIM to use another mode when receiving (Disable, set new configuration, then Enable).

 

Best regards,

Håkon

[taboteke]

Hi Håkon,

This is for write

nrf_drv_spi_init(&spi, &spi_config, NULL, NULL);
nrf_drv_spi_transfer(&spi, &ui8TxByte, 1, NULL, 0);

How about read? Can you give me an example how to do that?

Thanks and regards,

Leo

[Håkon Alseth]

Have a look at the $sdk_path/examples/peripheral/spi example. The two last parameters in nrf_drv_spi_transfer is the receive buffer and size.

 

Best regards,

Håkon

[taboteke]

Hi Håkon,

If the 2 last parameters was supplied, then read operation will occurred immediately, didn't it?

In my case there must be an action (change spi mode) before read.

Regards,

Leo

[Håkon Alseth]

Hi,

 

If the last two parameters are used as well, it will do a read and a TX at the same time (full duplex operation).

In your case, you transmit over SPI, then switch mode, then only receive over SPI (passing NULL,0 as the 2nd and 3rd input parameter and passing a valid buffer + size as 4th and 5th parameter).

 

Best regards,

Håkon