Sorry for the double post. But I wanted to ask a question, not start a discussion. So please ignore the other post. Perhaps a forum moderator could delete the other post.
I've got a custom board with an FPGA and 8 AD9915 of which I am trying to sync. I've attached a bock diagram how they are connected. Because of limited resources two AD9915 share one 32 bit Databus. They are addressed with the IOCFG signals. Each AD9915 has its' own I/O Update signal from the FPGA. All signals seem OK and the timing for the 32 bus is according to the datasheet. I followed the synchronization procedure according to the AN-1254 application note. However it seems that the chips are not synced. If I try to program the same frequency to each chip I can see phase offsets between each chip and the phases are jumping around every time I reprogram the chips. I programmed the frequency/amplitude values via the parallel port using Profile register 0. Are there any known problems with synchronising the chips?