LMX2694-SEP: Cannot write to the control registers of the PLL RF synthesizer LMX2694-SEP

Tool/software:

I cannot write to the control registers of the PLL RF synthesizer LMX2694-SEP even though the clock and timing of SPI signals are properly set.  I declare my variable as "volatile int8_t txData" as suggested.

Has anyone come across this issue and figured out the fix?

Thanks in advance.

Note: My SPI clock is set to 500 KHz; the first pulse is set after chip select (CS#) signal is pull low and timing are similar to the Figure 6-2 in the LMX2694-SEP datasheet, page 9.