Flexible memory controller (FMC) RM0090
1652/1749 RM0090 Rev 18
implement the prewait functionality needed by some NAND Flash memories (see
details in Section 37.6.5: NAND Flash prewait functionality).
6. The controller waits for the NAND Flash memory to be ready (R/NB signal high), before
starting a new access to the same or another memory bank. While waiting, the
controller holds the NCE signal active (low).
7. The CPU can then perform byte read operations from the common memory space to
read the NAND Flash page (data field + Spare field) byte by byte.
8. The next NAND Flash page can be read without any CPU command or address write
operation. This can be done in three different ways:
– by simply performing the operation described in step 5
– a new random address can be accessed by restarting the operation at step 3
– a new command can be sent to the NAND Flash device by restarting at step 2
37.6.5 NAND Flash prewait functionality
Some NAND Flash devices require that, after writing the last part of the address, the
controller waits for the R/NB signal to go low. (see Figure 457).
Figure 477. Access to non ‘CE don’t care’ NAND-Flash
1. CPU wrote byte 0x00 at address 0x7001 0000.
2. CPU wrote byte A7~A0 at address 0x7002 0000.
3. CPU wrote byte A16~A9 at address 0x7002 0000.
4. CPU wrote byte A24~A17 at address 0x7002 0000.
5. CPU wrote byte A25 at address 0x7802 0000: FMC performs a write access using FMC_PATT2 timing
definition, where ATTHOLD ≥ 7 (providing that (7+1) × HCLK = 112 ns > t
WB
max). This guarantees that
NCE remains low until R/NB goes low and high again (only requested for NAND Flash memories where
NCE is not don’t care).
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