Texas Instruments LMH0318 Programmer's Manual page 12

Device Configuration
4.2.8 Eye Opening Monitoring Operation
The LMH0318 has an on-chip eye opening monitor (EOM) which can be used to analyze, monitor, and
diagnose the performance of the link. The EOM operates on the post-equalized waveform, just prior to the
data sampler. Therefore, it captures the effects of all the equalization circuits within the receiver.
The EOM monitors the post-equalized waveform in a time window that spans one unit intervals and a
configurable voltage range that spans up to ±400 mV differential. The time window and voltage range are
divided into 64 steps, so the result of the eye capture is a 64 × 64 matrix of "hits," where each point
represents a specific voltage and phase offset relative to the main data sampler. The number of "hits"
registered at each point needs to be put into context with the total number of bits observed at that voltage
and phase offset in order to determine the corresponding probability for that point. The number of bits
observed at each point is configurable.
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 0-V differential amplitude, typically
measured in unit intervals or pico-seconds. 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 followings are the steps required to read eye hits for
64 × 64 cells or total 4096 cells.
RAW FF 04
RAW 11 00
RAW 24 80
RAR 24 00
RAW 26 xx
RAR 24 00
RAW 26 xx
RAR 24 00
RAW 25 xx
RAW 26 xx
RAW 24 00
RAW 11 20
12
LMH0318 Programming Guide
07 //Select Channel Registers
20 //Enable EOM
80 // Start Fast EOM
01 //Wait until EOM samples ready (0x24[0]= 0'b)
00 //Read Reg 0x26 and discard the content
01 //Wait until EOM Samples Ready
00 //Read Reg 0x26
01 //Wait until EOM Samples Ready
FF //Read Reg 0x25 and save number of eye hits
FF //Read Reg 0x26 and save number of eye hits
//Execute the above three commands for 4095 times (total 4096 times for
64X64 cells)
80 //Disable fast EOM
20 //Power down EOM
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SNLU183 – September 2015
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