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AD9910 Auto I/O-Update

Question asked by AndiN on Jun 4, 2012
Latest reply on Jun 11, 2012 by AndiN

I have trouble initializing the Auto-I/O-Update-Feature of the AD9910 on an eval board. My hardware can not control the external I/O-Update-Pin, which is left floating since it will be configured as an output in auto-i/o-update-mode. What i do is the following:

 

- issue a Master Reset and wait for 100ms

- load CFR3 with settings that results in SysClk=1GHz from ext. RefClk=10Mhz

- load I/O-Update-Register with a value that results in a 10µs update interval @ SysClk=1GHz

- load CFR2 with default settings + "Auto-I/O-Update Bit 23 =high"

- load all Profiles with different FTWs

 

How the device responds depends on the status of the Profile-Pins:

 

P0-P2 = 000b: Nothing happens.

No I/O-Update pulses on the I/O-update-pin, PLL_LOCK stays low and consequently no output signal is visible. Depending on the ext. Ref-Clk Amplitude either accurate 2.5MHz slopes are visible on SYNC_CLK or a signal apparently resulting from a lot of missed zero-crossings is visible (observed pulse widths are integer multiples of 1/2.5MHz).

 

P0-P2 != 000b: Everything works.

I/O-Update-pulses are visible with a 10µs interval, the PLL_LOCK is high and the output frequency of the selected profile is visible at the output. A 250Mhz-Signal is visible at SYNC_CLK and new values written to the Profile-Registers are immediately (10µs later) updated.

 

In the first case, the device can be made to work by changing the status of the profile pins to a value different from 000b or forcing I/O-Update high (touching with 3.3V-cable).

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