This is my first time using a DAC1220. I am using it to drive the OCXO (set the frequency) in a GPSDO. I believe I have gone through the initialization process, but somehow it's not working properly. It appears that it is staying in two's complement mode, instead of going to binary mode. IOW, the generated DAC should be about 0x80000 (20-bit mode) for mid scale. But, I'm getting a lock near 0x27A00. As I manually increment the DAC values, it suddenly goes down to min frequency, seeming to verify that it has not accepted the initialization command 0x20A0 to give me 20-bit resolution, straight binary.
I am controlling this with a dsPIC33FJ128MC802, if that matters. I'm applying 2.5MHz to the DAC1220, and setting the clock rate to about 208.333 KHz. Note that I am adding this to an existing GPSDO of my design. The existing hardware uses a PDM (Pulse Density Modulator) generated by the chip's motor control circuitry, so I already have a good idea of what values to expect for the DAC voltage. Any help would be appreciated.
Bob
