Calculating NAND Read Time – KBA223431

Version: **

 

Question:

Datasheet mentions random access time of Cypress flash as 25 µs. Is this the actual time to read a page?

 

Answer:

Random access time of 25 µs mentioned in the datasheet corresponds to the timing parameter tR (Read Cache busy time). It is the time the NAND flash will take to move memory contents from memory array to an internal cache register. The data is still required to be read out one-by-one. Calculate the actual page read time as shown below:

For example, see the page read timing diagram for the part S34ML01G2.

Total page read time will be the sum of the following specifications:

  1. Time for command 00h = tWC
  2. Time for Column Address = 2 x tWC
  3. Time for Row Address = 3 x tWC
  4. Time for command 30h = tWC
  5. Time for data transfer from cell to register = tR
  6. Time for ready to RE# low = tRR
  7. Time to read the page content = page size x tRC

So, the total time for page read will be:

Total PAGE READ time = (7 x tWC) + tR + tRR + (page size x tRC)

                                      = (7 x 25) ns + 25 µs + 20 ns + (2112 * 25) ns = ~ 78 µs

 

Note that the above calculation is for an ideal case. In real applications, the page read time will be higher than 78 µs in real applications.