DocID018909 Rev 11 1639/1731
RM0090 Flexible memory controller (FMC)
1669
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 455).
Figure 475. 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).
When this functionality is required, it can be ensured by programming the MEMHOLD value
to meet the t
WB
timing. However any CPU read or write access to the NAND Flash memory
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