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AMC7924: A question about BYPx registers for AMC7904, seems BYPx not work

Gene Chang
Prodigy 10 points
Part Number: AMC7924
Other Parts Discussed in Thread: AMC7904

Tool/software:

We have a question regarding the operation of a register.

According to the AMC7904 specification (Version SBAS882 – December 2018), specifically Figure 61: AMC7904 Data Path and Section 7.4.2.3: ALU Bypass,

we intended to set the BYP register, expecting that the DACxLUT value would be the same as DACxBASE.

However, based on the following operations, it appears that the ALU is still active, even when LUTDIS=1 is set to disable the ALU engine.

The DACxLUT value still does not match DACxBASE as expected.

Below are the detailed register operations:

=====Steps=====

First, we set and display the current DAC0BASE value, which is 0x1420.

Display all Page 4 register values as follows:

Then, set all BYP registers to 1.

Display the DAC0LUT value, and we observe that DAC0LUT is 0x1408, which is different from DAC0BASE, which is 0x1420.

We also verified that LUTSTAT is disabled. As for other configuration and status-related registers, their settings are as follows:

Could you please advise whether there is a misunderstanding on our part or if there is an issue with our operation?

We would appreciate any suggestions you can provide.

Thank you!

  • 0
    TI__Genius 11280 points

    Hi Gene,

    We received a similar message on the internal forum, so I'll send the same reply here:

    When using the overwrite code, the DAC will take the value from the DACx OVERWRITE registers on page 2 (Registers 0x08, 0x0A, 0x0C, 0x0E). The DAC_LUT readback will always show the ALU output. The intended use of the overwrite code is to bypass the ALU/LUT entirely and operate the DACs solely on data from the overwrite registers. In this case, the data in DAC BASE will not matter. If you put your DAC base code into the DAC Overwrite register, then the overwrite will set your DAC output to the base code. You should read back the active DAC code in the DACx registers (0x00, 0x02, 0x04, 0x06).

    Let me know if you have any other questions.

    Thanks,
    Erin