Pre/Post Cursor Analysis can be used to determine
an optimum setting for pre-emphasis in the transmitter.
- Program JESD_EN = 0 if necessary. Program EQMODE = 1. Program JESD_EN = 1 and allow sufficient time for the equalizer to adapt and
settle. You can read EQLEVEL_S multiple times to verify the value is stable or toggling
between adjacent values.
- Set EQHOLD = 1 to lock the equalizer (disable adaptation). This also
causes EQOVER and EQUNDER fields to become low.
- Wait at least 48UI, and proportionally longer if the CDR activity is less than
100% so the 1 on EQHOLD is sampled and acted upon. The SPI is slow enough that no
explicit delay is be necessary.
- Set EQMODE to 2 or 3 to select pre or post cursor analysis respectively.
With a separate SPI transaction, set EQHOLD = 0. The equalization characteristics of the received signal
are analyzed (the equalizer response continues to be locked).
- Wait at least 150,000UI to allow time for the analysis to occur, proportionately
longer if the CDR activity is less than 100%
- Examine EQOVER and EQUNDER for results of analysis:
- EQOVER high indicates the signal is over equalized;
- EQUNDER high indicates the signal is under equalized;
- Set EQHOLD = 1
- Adjust the transmitter pre-emphasis and repeat steps 3 thru 7 if required.
- Set EQMODE = 1, and with a separate SPI transaction, set EQHOLD = 0 to exit analysis mode and return to normal adaptive
equalization.