Other Parts Discussed in Thread: LMX2491
Dean,
I have finally written my own controller for the LMX2492. I can write to the device and read back correct values in the registers. I have the system connected to my Spectrum Analyzer and I see the signal in the correct location for all settings except ramp functions. The way I load things is with 1,2, or 3 registers at a time (instead of the long write of all registers). This works fine for multiple register settings, like fastlock reg's and setting N (which is spread over multiple registers).
But when I program ramp settings (reg141 - reg 86), the PLL loses lock. I am trying to make a sawtooth, just have 2 legs. I can watch it happen, I load, say, all ramp0 reg's, and by the time I'm done, the PLL output is down at the bottom rail. The registers have been written correctly, I can read them back. But the loop is not locked. It happens everytime. I can do a reset command, to load in a .txt file of settings saved from TCS, where all the ramp reg's are filled with 0s. After this reset I am locked on at the right frequency. But I'll try to program the ramp again and have the same problem. I have checked that the RAMP_EN is low before and during the loading of ramp registers. It really is. I have also tried to program things while the LMX is off, thinking maybe the loop won't drift if the output is off during the register writing. But this didn't work either.
How can I load the ramp registers without losing lock?
Thanks,
Darren