Auto clear sweep and phase accumulators


I'm a little confused in the use of  the auto clear phase accumulator 
and auto clear sweep accumulator bits.

A have few questions about this:

1.What is difference in the use of bits  FR[12..15] and CRF[0..3]

and how  to  set these bits in the  frequency sweep mode for one channel.

2. From the data sheet of AD9958/59 it follows that:  "The automatic clearing function is
repeated for every subsequent I/O update or change in profile pins until the clear and release bits are reset
I/O update or change in profile pins  via the serial port" (page 27).

It is not clear what kind of change in a profile pin have in mind.
For example consider "LINEAR SWEEP MODE ENABLE—NO-DWELL BIT SET" (Fig 38).

The signal P2 on profile pin changed twice during the sweep interval -  (at point A, he rises and between points A and B, it falls).
It is logical to assume that clearing takes place only on the rising edge, but I would like to know exactly.

3. In the  frequency sweep mode I use I/O update within sweep interval to change signal amplitude.

   Does this mean that the phase accumulator (or sweep accumulator) will be immediately cleared?

Many thanks for your advice.


  • 0
    •  Analog Employees 
    on May 9, 2011 9:45 PM over 9 years ago

    Hi Vlad,

    Bits <15:12> in Function Register 2 are global bits. This means all channels (phase accumulator and/or sweep accumulators) will be affected. So,to impact only one channel use bits <4:1> in the Channel Function Register.

    In most of ADI's DDSs, a profile change is equivalent to issuing an IO_UPDATE, however not in the multi-channel DDS (AD9958 or AD9959). Page 27 under Clear and Release Bits is in error, only the IO_UPDATE does the clearing, not a profile pin change.

    If the phase accumulator clear bits (auto/manual) or sweep accumulator clear bits (auto/manual) are set on any channel, an IO_UPDATE will reset accumulator each time it's issued.

  • 0
    •  Analog Employees 
    on Aug 2, 2018 4:21 PM over 2 years ago
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

    Thank you,
    EZ Admin