Sending data using SPI

Question

Hi all,

I need help sending data to a chip using the arduino SPI. The chip I am working with is the LMP91200 (Here is the link for the spec sheet http://www.ti.com/lit/ds/symlink/lmp91200.pdf, see bottom of page 18) whose serial interface uses a 16 bit shift register to recieve data. The arduino on the other hand uses SPI.transfer which sends in a byte at a time. Does anyone have any clue on how I can send in my data properly? For example I want to send in the 0000011100000000. I am using an Arduino micro.

Thanks,

Omar

shabaz · Answer

Often, if a target device needs a non-standard (i.e. not 8-bit) serial stream, then it is easier to just write a simple routine to

'bit-bang' the data yourself.

Basically, you need to translate the requirements from the timing diagram in the datasheet into code that will manipulate the

I/O to achieve the correct interface.

Here is an example. It's not an efficient method, but is a useful hack at times.

Note this is just a simple pseudocode example, not necessarily matching the requirements of your device. You can see that the

function accepts two bytes, and transmits them one after the other.

void write(unsigned char val[2])

{

unsigned char i, v;

for (v=0; v<2; v++)

{

for (i=0; i<8; i++)

{

if (val[v] & 0x80)

{

DATA_SET_HIGH;

}

else

{

DATA_SET_LOW;

}

msec_delay(1);

CLOCK_SET_HIGH;

msec_delay(1);

CLOCK_SET_LOW;

msec_delay(1);

val[v] <<= 1;

} // end for (i..

} // end for (v..

msec_delay(10); // delay after two bytes

}