Hi,
I'm using the AD9914 evaluation board, and I need clarification on the correct/intended procedure for switching from full USB control to partial external control.
Application context:
My workflow requires two phases per cycle:
- Program all internal registers over USB (FTW, DRG step/rate registers, CFR1/CFR2, profile registers, etc.) using the eval board GUI.
- Hand off control of DRCTL and PS0 to an external pattern generator for pulse-to-pulse triggering of the digital ramp generator, without the onboard USB microcontroller interfering on those lines.
The pins DROVR, DRHOLD, PS1 and PS2 are pulled to ground to ensure all externally controlled signals are not floating.
What I've observed from the schematic:
The P205 header block sits between U200 (USB microcontroller) and the AD9914 control/programming pins, and appears to be the intended isolation point. I'm currently removing/disabling P205 before starting my external pattern to avoid bus contention, and this has worked empirically — but I don't have documentation confirming this is the correct mechanism.
Specific questions:
- Is physically tri-stating/removing P205 (and possibly P203/P204) the ADI-recommended way to release the AD9914's control pins for external drive, or is there a GUI/software command that should be issued first (e.g., an "external control" or "release bus" mode) before pulling the header?
- Is there a required sequence — e.g., must the final IO_UPDATE be issued and registers latched before removing the jumper, or does the AD9914 need to be held in a defined state while the jumper is pulled, to avoid glitching DRCTL/PS0/IO_UPDATE?
- Are U202/U203/U204 (the 74LVC541APW buffers on DRCTL/IO_UPDATE per the schematic) actually tri-statable outputs controlled by the P20x headers, or is the header simply breaking a physical trace connection? This matters for understanding whether any pin floats to an undefined level (no pull resistors are shown on these lines) when the header is removed.
- What is the safe procedure to reconnect P205 and resume USB control afterward — does U200 need a reset/re-enumeration, or does it resynchronize automatically?
- Is this handoff procedure documented anywhere? (I haven't found it in the AD9914 datasheet)
Any confirmation from ADI application engineers or others who've used this board in a hybrid USB/external-control configuration would be greatly appreciated.
Thanks,
wmcher
