DS125DF1610 Datasheet, PDF (21/81 Pages) Texas Instruments – 9.8 to 12.5 Gbps 16-Channel Retimer

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DS125DF1610
SNLS482A – APRIL 2014 – REVISED DECEMBER 2015
7.3.12 Debug Features
7.3.12.1 Pattern Generator
Each channel in the DS125DF1610 can be configured to generate a 16-bit user defined data pattern or a pseudo
random bit sequence (PRBS). The user defined pattern can also be set to automatically invert every other 16-bit
symbol for DC balancing purposes. The DS125DF1610 pattern generator supports the following PRBS
sequences:
• PRBS – 2⁷ - 1
• PRBS – 2⁹ - 1
• PRBS – 2¹⁵ - 1
• PRBS – 2³¹ - 1
7.3.12.2 Pattern Checker
The pattern checker can be manually set to look for specific PRBS sequences and polarities or it can be set to
automatically detect the incoming pattern and polarity.
The pattern checker consists of a 47-bit word counter and an 11-bit error counter. The pattern checker uses 32-
bit words.
In order to read out the bit and error counters, the pattern checker must first be frozen. Continuous operation with
simultaneous read out of the bit and error counters is not supported in this implementation.
7.3.12.3 Eye Opening Monitor
The DS125DF1610’s Eye Opening Monitor (EOM) measures the internal data eye at the input of the CDR and
can be used for 2 functions:
1. Horizontal Eye Opening (HEO) and Vertical Eye Opening (VEO) measurement
2. Full Eye Diagram Capture
The HEO measurement is made at the 0V crossing and is read in channel register 0x27. The VEO measurement
is made at the 0.5 UI mark and is read in channel register 0x28. The HEO and VEO registers can be read from
channel registers 0x27 and 0x28 at any time while the CDR is locked. The following equations are used to
convert the contents of channel registers 0x27 and 0x28 into their appropriate units:
• HEO [UI] = ch reg 0x27 ÷ 64
• VEO [mV] = ch reg 0x28 x 3.125
A full eye diagram capture can be performed when the CDR is locked. The eye diagram is constructed within a
64 x 64 array, where each cell in the matrix consists of an 16-bit word. Users can manually adjust the vertical
scaling of the EOM or allow the state machine to control the scaling which is the default option. The horizontal
scaling controlled by the state machine and is always directly proportional to the data rate.
When a full eye diagram plot is captured, the retimer will shift out 4 16-bit words of junk data that should be
discarded followed by 4096 16-bit words that make up the 64 x 64 eye plot. The first actual word of the eye plot
from the retimer is for (X, Y) position (0,0). Each time the eye plot data is read out the voltage position is
incremented. Once the voltage position has incremented to position 63, the next read will cause the voltage
position to reset to 0 and the phase position to increment. This process will continue until the entire 64 x 64
matrix is read out. Figure 4 shows the EOM read out sequence overlaid on top of a simple eye opening plot. In
this plot any hits are shown in green. This type of plot is helpful for quickly visualizing the HEO and VEO. Users
can apply different algorithms to the output data to plot density or color gradients to the output data.
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