MOSI stays high after data transfer

edsonsanchez — Wed, 20 Aug 2014 17:23:12 GMT

Hi,

I am using the k40 and I am trying to communicate with another chip from Linear Technology. I am looking at the SPI signals coming out of the k40 and I notice that the MOSI pin stays high after the data has been sent out. I want it to remain low after data transmission... Does anybody know how to do this?

I am using the MQX SPI example and have modified it to communicate with the LT chip.

Thanks!

Re: MOSI stays high after data transfer

RadekS — Fri, 22 Aug 2014 12:45:01 GMT

Hi, I am not sure why you want such thing, but unfortunately this cannot be solved by any SPI configuration. SOUT signal always return to high logic in idle state.

option: you can invert whole output signal by external inverter (like 74HC14). However I suppose that, you don’t want take care on inverting values on master or slave side.
option: you can switch pin multiplex to GPIO during time when SOUT is inactive.

Best way how to do is create Chip select function which will be called at begin and at end of transfer.

For example (TWR-K40D100M, SPI0, I configured SOUT pin to input with pulldown):

#define BSP_SPI_MEMORY_SPI_CS 1

_mqx_int set_CS (uint32_t cs_mask, void *user_data)

{

PORT_MemMapPtr pctl;

pctl = (PORT_MemMapPtr)PORTD_BASE_PTR;

pctl->PCR[2] |= PORT_PCR_PE_MASK; /* enable pull-up/down*/

if (cs_mask & BSP_SPI_MEMORY_SPI_CS)

{

pctl->PCR[2] = PORT_PCR_MUX(2)|PORT_PCR_PE_MASK; /* DSPI0.SOUT */

}

else

{

pctl->PCR[2] = PORT_PCR_MUX(1)|PORT_PCR_PE_MASK; /* DSPI0.SOUT as GPIO */

}

return MQX_OK;

}

Inside task:

spifd = fopen (TEST_CHANNEL, NULL);

callback.CALLBACK = set_CS;

if (SPI_OK == ioctl (spifd, IO_IOCTL_SPI_SET_CS_CALLBACK, &callback))

{

printf ("Setting CS callback ...OK\n");

}

…write to SPI

Have a great day,
RadekS

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MOSI stays high after data transfer

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