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Fast NCO switching with AD6688 / AD6902

Category: Datasheet/Specs
Product Number: AD6688


I'm trying to operate the Fast NCO switching feature of AD6688 / AD6902 on 5 different phases with no success.

I'll explain what I did so far : 

Step 1 :

Calculate 5 FTWs and set each in the appropriate NCO channel :

1. Chose NCO channel to update by setting Bits[3:0] in the NCO control registers 0x0374.

2. Calculate the FTW using this formula :   (page 49 in the Data Sheet) and setting the 48bits word into registers : 0x0376 to 0x037B.

3. Repeat steps 1 through 2 for all other 4 channels.

Step 2 : 

Chose the GPIO option for transferring between channels - GPIO_B1 in Edge Control Mode : 

1. Wrote 0x0 to Bits[7:4] in Register 0x0042.

2. Configured the NCO channel selector in GPIO edge control mode by setting Bits[7:4] in the NCO control registers 0x0374 to 0xB.

3. Configured the wrap point for the NCO channel selection by setting Bits[3:0] in the NCO control registers 0x0374 to 4.

Step 3 :

Toggling GPIO_B1 0>1

Questions : 

1. What am I doing wrong ?

2. Does setting the selector - red circled FTW/POW write index (in the below Figure 75.) is by writing to register 0x0374 bits [3:0] ?

Thank you

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[edited by: KobiP at 11:09 AM (GMT -4) on 4 Sep 2023]