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Super Contributor
xilant
Posts: 170
Registered: ‎08-13-2007
0

Spartan-3A DCM frequency align mode

Hi
 
is it supported? and pointers or info?
the only reference for this mode is for Spartan-3E,
 
Antti Lukats
Visitor
alexhd
Posts: 5
Registered: ‎03-22-2013
0

Re: Spartan-3A DCM frequency align mode

5.5 years later....

Hi,

i try to run the frequency generator from http://www.xilinx.com/products/boards/s3estarter/files/s3esk_frequency_generator.pdf on the Sparten3A development board.

I change the DCM_x1y1 to DCM_x1y3 in the ucf file and also  in the bitget command:

-g cfg_dfs_s_x1y3:1111000011111111xxx111xxxxx1xxxxxxxxxx1xxxxxxxxxxxxxxxxxxxxxxxxxxxxx01000000.

 

But it seems i missing something because i get lot of jitter on the output pin.

In the code, i also change from

use IEEE.STD_LOGIC_ARITH.ALL;

use IEEE.STD_LOGIC_UNSIGNED.ALL;

to the

use IEEE.numeric_std.all;

with some change from std_logic_vector to unsinged. ( but the frequency is as expected, so i think i make there no mistakes)


Have anyone a idea what is wrong?

 

greetings

alex

 

Expert Contributor
bassman59
Posts: 6,084
Registered: ‎02-25-2008
0

Re: Spartan-3A DCM frequency align mode


alexhd wrote:

5.5 years later....

Hi,

i try to run the frequency generator from http://www.xilinx.com/products/boards/s3estarter/files/s3esk_frequency_generator.pdf on the Sparten3A development board.

I change the DCM_x1y1 to DCM_x1y3 in the ucf file and also  in the bitget command:

-g cfg_dfs_s_x1y3:1111000011111111xxx111xxxxx1xxxxxxxxxx1xxxxxxxxxxxxxxxxxxxxxxxxxxxxx01000000.

 

But it seems i missing something because i get lot of jitter on the output pin.

In the code, i also change from

use IEEE.STD_LOGIC_ARITH.ALL;

use IEEE.STD_LOGIC_UNSIGNED.ALL;

to the

use IEEE.numeric_std.all;

with some change from std_logic_vector to unsinged. ( but the frequency is as expected, so i think i make there no mistakes)


Have anyone a idea what is wrong?

 

greetings

alex

 


DCMs don't attenuate jitter like a PLL.

 

Changing to numeric_std from std_logic_arith is of course the right thing to do, but it has nothing to do with jitter.

 

Are you trying to monitor the output clock? Are you using the usual ODDR2 clock-forwarding trick? What does the input clock look like?


----------------------------------------------------------------
Yes, I do this for a living.
Visitor
alexhd
Posts: 5
Registered: ‎03-22-2013
0

Re: Spartan-3A DCM frequency align mode

Hi,

 

>> DCMs don't attenuate jitter like a PLL.

As in the linked pdf on page 11 described the dcm should only use the frequency information and produce a jitter "free" signal in the frequency aligned mode or not?

Is this mode not available on the Spartan3A? I did not found further information about this.

 

>> Are you trying to monitor the output clock?

>> Are you using the usual ODDR2 clock-forwarding trick?

 

I put the signal on the sma output pin of the development board (as was done in the example code) . Without the ODDR2 clock-forwarding trick. i connected the sma output pin to an oscilloscope.

 

>>What does the input  clock look like?

I dont monitor the input clk. I use the onboard 50 MHz.

Expert Contributor
bassman59
Posts: 6,084
Registered: ‎02-25-2008
0

Re: Spartan-3A DCM frequency align mode


alexhd wrote:

>> DCMs don't attenuate jitter like a PLL.

As in the linked pdf on page 11 described the dcm should only use the frequency information and produce a jitter "free" signal in the frequency aligned mode or not?

Is this mode not available on the Spartan3A? I did not found further information about this.


Again, DCMs don't attenuate jitter like a PLL.


>> Are you trying to monitor the output clock?

>> Are you using the usual ODDR2 clock-forwarding trick?

 

I put the signal on the sma output pin of the development board (as was done in the example code) . Without the ODDR2 clock-forwarding trick. i connected the sma output pin to an oscilloscope.


Well, using the ODDR2 for clock forwarding is vital because who knows how the signal is routed in the FPGA.


----------------------------------------------------------------
Yes, I do this for a living.