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DS50PCI402: How to select / measure proper settings

WorkerBee
Prodigy 100 points
Part Number: DS50PCI402

I think i understand how this part works in general, i'll make some statements, please tell me where i'm wrong, or there is some nuance which i should consider.

the DEMx[1:0] pins control the Vod and De-emphasis, which affect the ouput drive of the channel

the EQx[1:0] pins control the EQ settings which are for modifying the input signal of the channel.

1) i should first evaluate the best EQ settings

2) in order to evaluate what are the best EQ settings, i should look at the output of the received channel at the transmitter with default DEM settings and choose the EQ settings which have the best eye.

3) with the best EQ settings, next evaluate the best DEM settings.

4) in order to evaluate what are the best DEM settings, i should look at the signal at the received signal at the destination and choose DEM settings which give the best eye.

5) how do you feel this device will help an 800mb signal driving sometimes a 1M cat7 cable with shielded rj45 to a 10M cat7 cable with shielded rj45? this device would be placed < 1" from an FPGA.

6) can you recommend settings for question #5?

  • 0
    TI__Expert 3075 points

    Hello WorkerBee,

    Hope you are well. I'll get back to you with feedback on this thread shortly.

    Best,

    Nick

  • 0 in reply to Nick Peabody
    TI__Expert 3075 points

    Hello WorkerBee,

    I am going to go through your statements and provide feedback for each one:

    WorkerBee said:

    the DEMx[1:0] pins control the Vod and De-emphasis, which affect the ouput drive of the channel

    the EQx[1:0] pins control the EQ settings which are for modifying the input signal of the channel.

    Refer to the internal block diagram for the DS50PCI402 here:

    The equalization block is effecting the output signal as well. The equalization block's goal is to boost some of the high frequency components that are attenuated in the transmission medium, while maintaining linearity for any presets that need to be passed through. 

    WorkerBee said:

    1) i should first evaluate the best EQ settings

    2) in order to evaluate what are the best EQ settings, i should look at the output of the received channel at the transmitter with default DEM settings and choose the EQ settings which have the best eye.

    3) with the best EQ settings, next evaluate the best DEM settings.

    4) in order to evaluate what are the best DEM settings, i should look at the signal at the received signal at the destination and choose DEM settings which give the best eye.

    Overall the approach is good, you want the minimum amount of DEM and VOD when optimizing EQ so DEM = 0 and VOD= 0 is recommended. 

    WorkerBee said:
    5) how do you feel this device will help an 800mb signal driving sometimes a 1M cat7 cable with shielded rj45 to a 10M cat7 cable with shielded rj45? this device would be placed < 1" from an FPGA.

    What is the intended data rate?

    Best Regards,

    Nick P.

  • 0 in reply to Nick Peabody
    Prodigy 100 points

    data rate = two groups of  3x800mb, 1x400mb

    also, i've been starting to play with the smb control,  when you assert ENSMB, am i correct in that this causes the settings to immediately change to the SMB defaults, ignoring what the settings were prior to ENSMB?  

    in the datasheet it says "The De-Emphasis level must be set when in SMBus mode"  what happens before this is done?

    right now i'm working on some hardware remotely, and when assert ENSMB i lose connection to my fpga (which was going through this ds50pci402) ,  after looking at the default values in the registers, i would have guessed that the defaults would have allowed a connection, but until i can look at it with a scope i can't know exactly what is going on, i was curious if the previous statment was hinting at something.

  • 0 in reply to WorkerBee
    TI__Expert 3075 points

    Hello WorkerBee,

    To answer your question 5 from before: 

    WorkerBee said:
    5) how do you feel this device will help an 800mb signal driving sometimes a 1M cat7 cable with shielded rj45 to a 10M cat7 cable with shielded rj45? this device would be placed < 1" from an FPGA.

    The DS50PCI402 has data rate optimized 3-stage equalization to 27 dB gain. Based on the typical loss of 10m of cat7 cable (estimate of~10db), the redriver will provide sufficient equalization for the application.

    WorkerBee said:
    also, i've been starting to play with the smb control,  when you assert ENSMB, am i correct in that this causes the settings to immediately change to the SMB defaults, ignoring what the settings were prior to ENSMB?  

    Upon assertion of ENSMB the RATE, EQx and DEMx functions revert to register control immediately. The EQx and DEMx pins are converted to AD0-AD3 SMBus address inputs. The other external control pins remain active unless their respective registers are written to and the appropriate override bit is set, in which case they are ignored until ENSMB is driven low. On powerup and when ENSMB is driven low all registers are reset to their default state. If PRSNT is asserted while ENSMB is high, the registers retain their current state.

    WorkerBee said:
    in the datasheet it says "The De-Emphasis level must be set when in SMBus mode"  what happens before this is done?

    right now i'm working on some hardware remotely, and when assert ENSMB i lose connection to my fpga (which was going through this ds50pci402) ,  after looking at the default values in the registers, i would have guessed that the defaults would have allowed a connection, but until i can look at it with a scope i can't know exactly what is going on, i was curious if the previous statment was hinting at something.

    Yes it is recommended. Each register (0x11, 0x18, 0x1F, 0x26, 0x2E, 0x35, 0x3C, 0x43) requires a De-emphasis settings when in SMBus mode.

    Best,

    Nick P.