AD8402 digital pot - sending 10bits via SPI?

rcooke · Joined: 23 Feb 2011 Posts: 21 Location: Oceanside, CA USA

Hi Folks,

In my application I am forced to use the HW SPI due to conditions out of my control. I need to write 10 bits to the chip 2 bits of address and 8 bits of data. I can't use the CCS supplied 8400.c library because that uses a software SPI.

Looking at the 8402 datasheet is seems like I can send it 16 bits with the MSB 6 bits set to zero. It seems like the chip will load the register when the /CS line goes high so only the last 10 bits are actually loaded. Does this make sense?

Thanks,

Richard

bkamen · Posted: Sun Apr 10, 2011 1:41 pm

That's pretty bizarre...

I would just write a software routine to handle it since doing a double write (16bits) doesn't seem to be an option.

How bizarre.

-Ben
_________________
Dazed and confused? I don't think so. Just "plain lost" will do. :D

rcooke · Joined: 23 Feb 2011 Posts: 21 Location: Oceanside, CA USA

I don't understand why you say it is bizarre. The hardware team designed the circuit in such a way that I am forced to use the hardware SPI function on the chip (18F24K22). We have other devices that I have to communicate with via the SPI bus.

Richard

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

rcooke · Joined: 23 Feb 2011 Posts: 21 Location: Oceanside, CA USA

PCM,

Thanks for the heads-up. I searched the forum but didn't do a very good job. I just wanted a second opinion and you pointed me to one. That's the beauty of this forum.

Richard

FvM · Joined: 27 Aug 2008 Posts: 2337 Location: Germany

There's a simple guideline. A device declared SPI compatible will always be able to communicate in multiplies of 8 bits. As many simple SPI devices, the AD8402 doesn't care how many bits have been shifted in front of the last 10 bits before the /CS rising edge.