SNAU305 February   2025 LMH1229 , LMH1239

 

  1.   1
  2.   LMH1229 and LMH1239 Programming Guide
  3.   Trademarks
  4. 1Access Methods
    1. 1.1 Register Programming Through SMBus
    2. 1.2 Register Programming Through SPI
    3. 1.3 Register Pages
  5. 2Register Command Syntax
  6. 3Device Configurations
    1. 3.1  Common Device Configuration
    2. 3.2  Common Register Commands
      1. 3.2.1 Channel Control
      2. 3.2.2 LMH12x9 Resets
        1. 3.2.2.1 LMH12x9 ENABLE Pin Override
        2. 3.2.2.2 LMH12x9 Share, CDR, and EQ/Drivers Page Resets
    3. 3.3  IN_MUX_SEL Override
    4. 3.4  Signal Detect Status for SDI_IN± and SDI_IN1±
      1. 3.4.1 Force Signal Detect Power Down
    5. 3.5  Lock Data Rate Indication
    6. 3.6  CDR Loop Bandwidth Override
    7. 3.7  Selective SMPTE Data Rate Lock
      1. 3.7.1 Digital Mute Reference Threshold
      2. 3.7.2 CTLE Index Check and Manual CTLE Override
    8. 3.8  Eye Opening Monitoring Operation
      1. 3.8.1 Fast EOM
        1. 3.8.1.1 Fast EOM Operation
      2. 3.8.2 Read Horizontal and Vertical Eye Opening
    9. 3.9  SDI_OUT±, OUT0± and OUT1± Default Mode of Operation
      1. 3.9.1 SDI_OUT±, OUT0± and OUT1± Independent Control
    10. 3.10 Invert OUT0±, OUT1±, and SDI_OUT± Data Polarity
    11. 3.11 OUT0±, OUT1±, and SDI_OUT± Driver Settings
      1. 3.11.1 OUT0± and OUT1± VOD Settings
      2. 3.11.2 OUT0± and OUT1± De-Emphasis Settings
      3. 3.11.3 SDI_OUT± VOD Settings
      4. 3.11.4 SDI_OUT± Pre-Emphasis
      5. 3.11.5 Output Driver Power Down
      6. 3.11.6 Cable Fault Detection (CFD)
    12. 3.12 LOCK_N Pin Output Settings
      1. 3.12.1 Interrupt Outputs Programmed by Interrupt Registers
    13. 3.13 PRBS Generator and Checker
    14. 3.14 CDR Lock Timing Control
      1. 3.14.1 Watchdog Timer
  7. 4Register Maps
    1. 4.1 Share Registers
    2. 4.2 CDR Registers
    3. 4.3 EQ_Drivers Registers

3.8.2 Read Horizontal and Vertical Eye Opening

A common measurement performed by the EOM is the horizontal and vertical eye opening. The Horizontal Eye Opening (HEO) represents the width of the post-equalized eye at the zero-crossing, typically measured in unit intervals or picoseconds (ps). The Vertical Eye Opening (VEO) represents the height of the post-equalized eye, measured midway between the mean zero crossing of the eye. This position in time approximates that of the CDR sampling phase.

The LMH12x9 produces two readings to indicate line signal quality. These parameters can be read by the host processor, or the LMH12x9 can be optioned to cause an interrupt if HEO/VEO reaches a predetermined threshold. See the equation below to convert the HEO reading to UI (Unit Interval) eye opening.

Equation 1. HEO = (Decimal Reg 0x6A) / 64

For example, if the HEO reading is 0x31 (49 decimal), then the HEO UI eye opening is 49/64 = 0.77 UI. This means the HEO is about 77% open.

Similarly, VEO has 64 steps as well. The chip automatically covers ±400mV thus, each step is 800/64, or 12.5mV. See the equation below to convert the VEO reading to a voltage measurement.

Equation 2. VEO inmV = (Decimal Reg 0x6B) × 12.5

For example, if we read 0x50 (32 decimal) for the VEO reading, this corresponds to 32 × 12.5mV = 800mV vertical eye opening.

Table 3-23 Horizontal and Vertical Eye Opening (HEO and VEO)
COMMANDREGISTERVALUEMASK//COMMENTS

RAW

FF

00

07

//Select Share Register Page

RAW

0B

02

02

//Force enable VCO clock to enable EOM counting
RAWFF0407//Select CDR Register Page
RAW

64

0080//Sets EOM power down to low, enabling EOM
RAW

64

00

40

//Scale EOM range - Custom scaling

RAW64

30

30

//12.5mV step

RAW

65

00

40

//Disables Fast EOM

RAW

67

02

02

//Enable eom_get_heo_veo to start HEO/VEO capture

RAW

FF

00

80

//Select Share Register Page

RAW

0B

00

02

//Force disable VCO clock to disable EOM counting

RAW

FF

04

07

//Select CDR Register Page

RAW

64

80

80

//Power down EOM capture

RAR

6A

FF

FF

//Read 8 bits of HEO

RAR

6B

FF

FF

//Read 8 bits of VEO

RAR

67

18

18

//Read Reg 0x67[4:3] for vrange setting