GD32F403xx User Manual
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devices. Each bank has a corresponding register to manage and control the external memory,
such as EXMC_NPCTLx, EXMC_NPINTENx, EXMC_NPCTCFGx, EXMC_NPATCFGx,
EXMC_PIOTCFG3 and EXMC_NECCx. Among these registers, EXMC_NPCTCFGx,
EXMC_NPATCFGx, EXMC_PIOTCFG3 registers contain four timing parameters individually
which are conf igured according to user specification and features of the external memory.
Table 21-17. NAND Flash or PC Card programmable parameters
Programmable parameter
W/R
Unit
Functional description
NAND Flash/
PC Card
Min
Max
High impedance time of the
memory data bus
(
HIZ
)
W/R
HCLK
Time to keep the data bus high
impedance after starting write
operation
0
255
Memory hold time
(
HLD
)
W/R
HCLK
The number of HCLK clock
cycles to keep address valid
after sending the command. In
write mode, it is also data hold
time.
1
254
Memory wait time
(
WAIT
)
W/R
HCLK
Minimum duration of sending
command
2
256
Memory setup time
(
SET
)
W/R
HCLK
The number of HCLK clock
cycles to build address before
sending command
1
255
The f igure below shows the programmable parameters which are defined in the common
memory space operations. The programmable parameters of Attribute memory space or I/O
memory space (only for PC Card) are defined as well.
Figure 21-23. Access timing of common memory space of PC Card Controller
Chip Enable
(EXMC_NCE)
EXMC_NREG
EXMC_NIORD
EXMC_NIOWR
Clock
(EXMC_CLK)
Address
(EXMC_A[25:0])
EXMC_NWR
EXMC_NOE
Write Data
Read Data
C 1 HCLK
COMHIZx HCLK
CO 1 HCLK
COMHLDx HCLK
Valid
NAND Flash operation