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HMC832 SPI protocol

Question asked by nlantz on Sep 16, 2016
Latest reply on Sep 16, 2016 by dyoung1

I am working with the HMC832LP6GE Evaluation Kit. I can get the PLL to program and output a frequency with the USB interface kit and PLL Eval Software. However, I have not been able to program it in our circuit. I hooked a logic analyzer up to the eval kit and discovered that the SPI Protocol does not match the timing diagram in the Datasheet.  Page 30. 


1. I found that the SEN pin is inverted. The signal on the evaluation kit is behaving as an enable high instead of an enable low. The diagram is a little confusing. It switches half way through the write. My team and I are interpreting the SEN signal in this diagram as an enable low. 


2. The data structure seems to be incorrect.

The structure I found is:

Ax Ax, R4 R3 …. R0, D23 D22 …. D0, Ax 


Where the datasheet calls the following structure:

D23 D22 …. D0, R4 R3 …. R0, Ax Ax Ax



A is the chip address. Always zeros

R is the Register address (R4 is MSB)

D is the Data (D23 is MSB)


I have attached a screenshot of a logic analyzer recording a write to enable RF_P. This was recorded using the Eval software by clicking the Enable RF_P check box. Using the  structure I found this decodes to the following:

Chip Address = 0x0

Register Address = 0x5

VCO Register Address = 0x3        D[3:0]

VCO Data = 0x19                           D[23:4] (Default || enable RF_P) 



Would someone please clarify the discrepancy between the datasheet and my measurements for me? We have not yet been able to program this chip with a micro-controller so I believe we are still missing something.