DS90UB929-Q1: how to enable CMM loop-through driver for DS90UB928?

Eric Li3

Prodigy 150 points

Part Number: DS90UB929-Q1
Other Parts Discussed in Thread: DS90UB928Q-Q1

hello sir,

i am eric.li, Electronic Engineer of Advantech co. ltd.

can you please guide us how to enable CMM loop-through driver for DS90UB928 step by step?

we tried to set add 0x56 to 00 but there is no output from pin44/45 (CMLOUTP/CMLOUTN) of DS90UB928?

is there any steps we lost to set?

thx!

Regards,

Eric Li

over 3 years ago

0 Eric Li3 over 3 years ago

Prodigy 150 points

hello sir,

we was able to enable CML loop-through by set 0x56 at 00.

we measured the eye diagram and the result is

Eh, Eye Height, 337.5 mV

Ew, Eye Width, 342.16ps

/resized-image/__size/320x240/__key/communityserver-discussions-components-files/138/676.png

referred to DS90UB928, it only mentions the typical values of Eh and Ew and did not mention min or max value.

/resized-image/__size/320x240/__key/communityserver-discussions-components-files/138/pastedimage1618465757544v1.png

can you guide us how to judge if the result is passed or not?

thx!

Regards,

Eric Li

0 Charley Cai over 3 years ago in reply to Eric Li3

TI__Genius 12866 points

Could you tell me the pixel clock frequency?

Best Regards,

Charley Cai

0 Eric Li3 over 3 years ago in reply to Charley Cai

Prodigy 150 points

hello Mr.Cai,

if the the pixel clock means the input to the pin49, 50 of DS90UB929, it is 65MHz. thx!

Regards,

Eric Li

0 Charley Cai over 3 years ago in reply to Eric Li3

TI__Genius 12866 points

Hi Eric,

In this case, the eye looks ok.

Best Regards,

Charley Cai

0 Eric Li3 over 3 years ago in reply to Charley Cai

Prodigy 150 points

hi Mr. Cai,

based on current pixel clock, 65MHz, can you give us the criteria?

for example, the minimum values of Eh and Ew.

Thx!

Regards,

Eric Li

0 Charley Cai over 3 years ago in reply to Eric Li3

TI__Genius 12866 points

Hi Eric,

We only have typ numbers for CMLOUT.

Best Regards,

Charley Cai

0 Eric Li3 over 3 years ago in reply to Charley Cai

Prodigy 150 points

hi Mr.Cai,

as your reply before, the eye looks ok.

how did you judge it? does it mean it is ok when Ew and Eh are greater than the typ number of CMLOUT?

thx!

Regards,

Eric Li

0 Charley Cai over 3 years ago in reply to Eric Li3

TI__Genius 12866 points

Hi Eric,

For 65Mhz PCLK, the whole eye width is 1/(65Mhz*35) = 440ps.

The Typical jitter in terms of UI is 0.4UI which translate to 176ps (440ps*0.4) of jitter. The remaining eye opening is 264ps.

The measured eye opening is better than the typical which means the eye is ok.

The eye height is also higher than the typical which is ok.

Best Regards,

Charley Cai

0 Eric Li3 over 3 years ago in reply to Charley Cai

Prodigy 150 points

Hi Mr.Cai,

understood,

one more question, as you replied "For 65Mhz PCLK, the whole eye width is 1/(65Mhz*35) = 440ps",

where is the parameter 35 from? why is 35?

thx!

regards,

Eric Li

0 Charley Cai over 3 years ago in reply to Eric Li3

TI__Genius 12866 points

35 is the number of bit in a FPD-Link forward channel frame. PCLK * 35 to get forward channel bit rate.

Best Regards,

Charley Cai

0 Eric Li3 over 3 years ago in reply to Charley Cai

Prodigy 150 points

hi Mr.Cai,

thanks for your explanation!

as you mentioned above, both the measured EyeWidth and EyeHeight are greater than the typical value and PASSED.

it seems it is more suitable to be a minimum value, not typical value.

are you able to revise the data sheet of DS90UB928Q-Q1? to move the Ew 0.4UI and Eh 300mV from column "typ" to "min". thx!

Regards,

Eric Li

+1 Charley Cai over 3 years ago in reply to Eric Li3

TI__Genius 12866 points

Hi Eric,

No, we will not revise the datasheet. The CMLOUT is sampled after RX EQ, so only typical value can be provided.

Best Regards,

Charley Cai

Interface

Interface forum

DS90UB929-Q1: how to enable CMM loop-through driver for DS90UB928?