creating an SPI clock output?

Hi all.

I'm using the MSP430FG4618 to control the TRF7970a NFC chip (by TI), hopefully making the two interact via SPI communication.

I'm quite new to MSP430, and I need to make a data_clk (aka SPI_CLK) triggering the SPI from the MCU to the NFC chip.

I have some sample code d/l from TI, showing how to create this clock, but it's not totally understandable to me, plus the clock signal is a bit jerky and has weird 'duty cycle' (see figure).

According to the NFC chip's manual, I need this duty cycle behavior for some reason, but I don't understand how is it controlled by the code.

SO - can anyone give me a code for a function that generates an SPI clock at about 2MHZ, and explain to me how to obtain this 'pull-down' behavior, like in this figure?

btw - output signal should be on P3.3

Thanks

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