Note: For data rates at or below 1,600 Mb/s, the
first two of the following calibration stages are skipped. At low data rates, the data
eye is wide enough that previous calibration stages provide adequate DQS
centering.
Read DQ Per-bit Deskew and Centering is performed over multiple stages. This maximizes the data eye and centers the internal read sampling clock in the read DQ window for robust sampling. To achieve this, Read Eye Training performs the following sequential steps:
- Maximizes the DQ eye by removing skew and On-Chip Variation (OCV) effects using per-bit read DQ deskew.
- Sweeps DQS across all DQ bits and finds the center of the data eye using both easy (Multi-Purpose register data pattern) and complex data patterns. Centering of the data eye completes for both the DQS and DQS#.
- Post calibration, continuously maintains the relative delay of DQS versus DQ across the VT range.