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LMH1219: VEO value is not changed by cable length

Part Number: LMH1219
Other Parts Discussed in Thread: SIGCONARCHITECT

Hello,

Make LMH1219 board to make Eye pattern, and under test now.

But there is some issue which  VEO value is not changed by cable length.

 -. Read 0x28 to calculate VEO as below code, but VEO value is not changed by cable length.

 -. VEO value with 75M and 1M are the same value at 3G input.

 -. VEO value at 3G and 12G input are different.

Question.

 -.  According to LMH1219 Programming Guide, VEO (0x28) has 64 steps.

 -. Does it mean 0x28 register used only 6bit [5:0]?

   

Regards,

Nicky

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Device ID(0xF1)          : 0x80

Device Revision(0xF0) : 0x02

 

             while(1)

             {

                           Write(0xff, 0x05);                                        //CableEQ/Drivers Register Page

                           Read(0x02, 1);                              //Get RATE

                           Write(0xff, 0x04);                                        //CTLE/CDR Register Page

                           Write(0x2c, 0x32);                                       //Set to Manual

                           Write(0x3e, 0x00);

                           Write(0x11, 0xc0);                                      //VEO SCALE=12.5mv

                           Write(0x23, 0xc0);                                      //Enable HEO/VEO Acquisition override

                           Write(0x24, 0x02);                                       //Disable Fast EOM & Acquire HEO/VEO

                           while(Read(0x24) & 0x02 !=0);       //wait for ready

                           Read(0x27, 1);                              //HEO                 Jitter <= 1.0-HEO/64

                           Read(0x28, 2);                              //VEO, SCALE    mV <= (VEO &0x3f) * SCALE_TABLE[((SCALE>>5)&0x03)]

                           Write(0x23, 0x40);                                       //Disable HEO/VEO Acquisition override                 

                           Write(0x3e, 0x00);                                      

                           Write(0x11, 0xc0);                                      //VEO SCALE=12.5mv

                           Write(0x24, 0xC1);                                      //Enable Fast EOM & Start EOM counter

                           while(Read(0x24) & 0x01 !=0);       //wait for ready

                           Read(0x29, 1);                              //SCALE(not use)

                           Read(0x25, 8192);                                        //Get EYE data

             }

 

  • Hi Nicky,

    LMH1219 has adaptive cable equalizer. This means LMH1219 state machine changes equalizer gain automatically in order to have as optimum eye opening at the output of the equalizer circuit block as possible. CDR or PLL portion of the the LMH1219 determines VEO to measure eye opening at the output of the equalizer circuit block(CDR is at the output of the equalizer circuit block). So it is possible that VEO and HEO could be the same between two different cable lengths since we have adaptive cable equalizer.

    Please follow LMH1219 programming guide. To calculate or measure VEO, we need to read reg 0x28, convert to decimal, and then multiply by 3.125mV. This provides vertical eye opening. You can also use SigconArchitect GUI as well to correlate with your own measurements.

    Regards,, Nasser