We are building a board with the IMX6UL and a MT41K128M16JT-125 DDR3L chip.
The datasheet for the DDR3L chip states that for speed grade 125 the data rate is 1600 MT/s. However the max speed of the DDR bus on the IMX6UL is stated as "up to 400MHz (800 MT/s)" (table 33-1 in the TRM).
In table 1 of the DDR3L chip it states that tRCD is 13.75ns for speed grade 125 at 1600 MT/s. There is not an entry for 800 MT/s. In table 29 it has entries for DDR3L-800 which are speed grades 25 / 25E, and it lists tRCD values for that in terms of clock ticks, giving 5 ticks for grade 25E and 6 ticks for grade 25, where 1 tick is 2.5ns, so 12.5ns for grade 25E or 15ns for grade 25.
That's three options I have to use for tRCD. The same applies for tRC and tRAS. I'm guessing I want to use one of the values for the DDR3L-800 but not sure if to use the grade 25 or grade 25E. I could try both, but I'd prefer to understand how this works and not just go with the faster one because it works on one board.
Thanks for any advice.