Nand Flash Pre-Wait Functionality; Figure 424. Access To Non 'Ce Don't Care' Nand-Flash - ST STM32F40 Series Reference Manual

RM0090
attribute memory space makes it possible to use a different timing configuration of the
FSMC, which can be used to implement the prewait functionality needed by some
NAND Flash memories (see details in
functionality on page
4. The controller waits for the NAND Flash to be ready (R/NB signal high) to become
active, before starting a new access (to same or another memory bank). While waiting,
the controller maintains the NCE signal active (low).
5. The CPU can then perform byte read operations in the common memory space to read
the NAND Flash page (data field + Spare field) byte by byte.
6. The next NAND Flash page can be read without any CPU command or address write
operation, in three different ways:
–
–
–
32.6.5

NAND Flash pre-wait functionality

Some NAND Flash devices require that, after writing the last part of the address, the
controller wait for the R/NB signal to go low as shown in

Figure 424. Access to non 'CE don't care' NAND-Flash

NCE
CLE
ALE
NWE
NOE
I/O[7:0]
R/NB
1. CPU wrote byte 0x00 at address 0x7001 0000.
2. CPU wrote byte A7-A0 at address 0x7002 0000.
3. CPU wrote byte A15-A8 at address 0x7002 0000.
4. CPU wrote byte A23-A16 at address 0x7002 0000.
5. CPU wrote byte A25-A24 at address 0x7802 0000: FSMC performs a write access using FSMC_PATT2 timing definition,
where ATTHOLD ≥ 7 (providing that (7+1) × HCLK = 112 ns > t
goes low and high again (only requested for NAND Flash memories where NCE is not don't care).
1362).
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
High
0x00 A7-A0 A15-A8
(1) (2) (3)
Doc ID 018909 Rev 4
Flexible static memory controller (FSMC)
Section 32.6.5: NAND Flash pre-wait
A23-A16 A25-A14
tWB
(4) (5)
max). This guarantees that NCE remains low until R/NB
WB
Figure 424.
NCE must stay low
tR
ai17733b
1362/1422