GD32F403xx User Manual
588
When EXMC sends command or address to NAND Flash, it needs to use the command latch
signal (A [16]) or address latch signal (EXMC_A [17]), namely, the CPU needs to perform
write operation in particular address.
Example: NAND Flash read operation steps:
1.
Conf igure EXMC_NPCTLx and EXMC_NPCTCFGx register. When pre-waiting is
needed, EXMC_NPATCFGx has to be configured.
2.
Send the command of NAND Flash read operation to the common space. Namely, during
the valid period of EXMC_NCE and EXMC_NWE, when EXMC_CLE (EXMC_A [16])
becomes valid (high level), data on the I/O pins is regarded as a command by NAND
Flash.
3.
Send the start address of read operation to the common space. During the valid period
of EXMC_NCE and EXMC_NWE, when EXMC_ALE (EXMC_A [17]) becomes valid
(high level), the data on the I/O pins is regarded as an address by NAND Flash.
4.
Waiting f or NAND ready signal. In this period, NAND controller will maintain EXMC_NCE
valid.
5.
Read data byte by byte from the data area of the common space.
6.
If new commands or address haven’t been written, data of the next page can be read
out automatically. You can also read the data of the next page by going to st ep 3 and
then writing a new address or writing a new command and address in step 2.
NAND Flash pre-wait functionality
Some NAND Flash requires that the controller should wait for NAND Flash to be busy after
the f irst command byte following the address bytes is send, and some EXMC_NCE-sensitive
NAND Flash also requires that the EXMC_NCE must remain valid before it is ready.
Taking TOSHIBA128 M x 8 bit NAND Flash as an example:
Figure 21-24. Access to none "NCE
don’t care" NAND Flash
Address Latch
Enable
(EXMC_A[17])
Write Enable
(EXMC_NWE)
Chip Enable
(EXMC_NCE)
Command Latch
Enable
(EXMC_A[16])
Output Enable
(EXMC_NOE)
Data
(EXMC_D[7:0])
Ready
(EXMC_INT[x])
tWB
tR
CMD 0
(00h)
CMD 1
30h
ADD 0
(CA0-7)
ADD 1
(CA8-11)
ADD 2
(PA0-7)
ADD 3
(PA8-15)
1.
Write CMD0 into NAND Flash bank common space command area.
Содержание GD32F403 Series
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