• State
  • Locked Locked
  • Replies 5 replies
  • Subscribers 32 subscribers
  • Views 1208 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DVB-ASI mode problem of LMH0070

user4793593
Prodigy 30 points
Other Parts Discussed in Thread: LMH0070

I am trying to outout DVB-ASI signals of MPEG-2 transport stream through LMH0070
using its DVB-ASI mode, but DVB-ASI stream analyzer connected to DVB-ASI output terminal
did not detect MPEG-2 transport stream.

I cheked registers via SMB bus and found a few questions. let me know if someone knows
the root cause of these problem.

1) My board connects 3.3V power line to DVB_ASI pin of LMH0070.
   I expect Mode register (address 0x21, bit [1:0]) would be "3" (DVB-ASI mode),
   but it is "0" instead. Is there any problem in the schematics of the board?.

   Also, Mode register did not change after I wrote "1" to RESET register (address 0x01, bit[0]).

   registers values after power up

          0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
    00: ae 00 05 05 04 00 00 01 03 bc 01 1c 01 bc 01 bc
    10: 01 bc 01 00 00 bc 01 62 00 00 00 00 00 fe 04 00
    20: 00 00 00 00 00 00 3f 00 04 00 0f 00 00 80 00 38   <<< 0x21 bit[1:0] Mode register=0
    30: 62 02 00 58 06 00 00 00 00 00 00 00 00 00 00 00
    40: 55 00 00 37 10 0f 38 40 02 7d c4 1a 80 03 1c 57
    50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    60: 0c 00 00 00 00 00 00 20 20 03 00 00 00 00 00 00
    70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

2)  I tried to change Mode by the following register write sequence and found Mode
   register was set to "3". but still DVD-ASI stream analizer did not detect MPEG-2 transport
   streams. so I think I failed to change operation mode of LMH0070.
   Is this sequence correct to change Mode?

   address   data
   0x21      0x3     (Mode)
   0x22      0x1     (DVB_ASI Override)
   0x26      0xBF    (channel reset)

3) Input pins TXCLK+, TXCLK-, TX[4:0]+, TX[4:0]- are connected to FPGA.
   I assume polarity of those input signals are "positive".
   Attached Simulation wave form shows signals of those input pins when
   Null packet (0x47 0x1F 0xFF 0x10 0xFF 0xFF ...) is put into LMH0070.
   Is there any problem regarding to this wave form?

  • 0
    TI__Guru* 93670 points
    Greetings,

    Thanks for the detailed description. I believe using pin control - like what you have done by pulling pin 6 DVB-ASI high - should be good enough to set the device in DVB-ASI mode. This can be done via registers as well but in default mode pin control should be able to put the device in DVB-ASI mode.

    One thing to note, in DVB-ASI mode TX4+/- is used as data valid bit. It also indicates lower and upper nibble of the 8b10b encoder. I am not sure if you are following this convention or it seem you may be using TX4+/- just as another data bit. Please let us know.

    Regards,,nasser
  • 0 in reply to Nasser Mohammadi
    Prodigy 30 points

    TX4+/- are kept H/L respectively while valid MPEG-2 transport packet signals are input to TX[3:0]+/TX[3:0]-, in this case both positive edges and negative edges of 188 consecutive 27MHz-CLK cycles. I think upper nibles and lower nibles are recognized by positive edges and negative edges of TXCLK+/-. 

  • 0 in reply to user4793593
    TI__Guru* 93670 points
    Greetings,
    I looked at this a bit more closely and as you noted clock high and low is used for high nibble and low nibble respectively.
    1). If TX4 is held low then we should be sending idle characters. Is idle characters being recognized by the MPEG decoder?
    2). Can we use scope probe to see if there is a repeating pattern or any activity on the output of the serializer when DVB-ASI pin is help high?
    Regards,,nasser
  • 0 in reply to Nasser Mohammadi
    Prodigy 30 points

    I observed several characters including K28.5 at the BNC connected to TXOUT+/- output pins by using scope, but K28.5 characters seem to be sent even if when TX4 was held high (TX4+/- = H/L). So I thought LMH0070 is not in DVB-ASI mode, or  maybe input signals polarity is wrong.

  • 0 in reply to user4793593
    TI__Guru* 93670 points

    Greetings,

    1). If K28.5 is being sent out when TX4 is low and these are note being generated by TX[3:0], i believe this means device is indeed in DVB-ASI mode. Can you please confirm this.

    2). How about if you use TXOUT- instead of TXOUT+ - to change polarity. Does this make a difference?

    Regards,,nasser