Having trouble using PIC as SPI driver for Hittite PLL

[The Altruist]

I'm working on a project where I'm using a PIC18F14K50 to drive a Hittite HMC704LP4E frequency synthesizer via SPI in HMC Mode. I'm trying to make sense of the Hittite documentation. Am I understanding it correctly that I DON'T send whole bytes to the Hittite chip, just strings of bits (in non-multiples of 8)? I don't have an eval board to work with, and I'm just the "code guy." Does anyone else have experience working with these?

[HenrikOlsson]

Hi,
I don't have any experience with these chips but I briefly looked at the datasheet. Indeed, the HMC mode does look "strange".

If you're using the bitbanged routines, ie SHIFTOUT/SHIFTIN then I don't think there shold be any problems shifting out/in any number of bits. However if you're using the MSSP module then HMC mode doesn't seem to be a good fit.

Is there a specific reason for selecting HMC mode? It seems easy enough to just select Open mode instead, in which case a transaction is 32 bits (24 + 5 + 3), if I'm reading the datasheet correctly. That mode looks a lot easier "to do" than HMC mode.

/Henrik.

[The Altruist]

Hm... you might be right. I completely over looked that. Let's see if it works!