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GD32F403xx User Manual
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in the EXMC_SNTCFGx register.
1. Data latency and NOR Flash latency
Data latency is the number of EXMC_CLK cycles to wait bef ore sampling the data. The
relationship between data latency and NOR Flash specification’s latency parameter is as
f ollows:
For NOR Flash’s specification excluding the EXMC_NADV cycle, their relationship should be:
NOR Flash latency=DLAT+2 (21-6)
For NOR Flash’s specification including the EXMC_NADV cycle, their relationship should be:
NOR Flash latency=DLAT+3 (21-7)
2. Data wait
Users should guarantee that EXMC_NWAIT signal matches that of the external device. This
signal is configured through the EXMC_SNCTLx registers, it is enabled by the NRWTEN bit,
and the active timing could be one data cycle before the wait state or active during the active
state by the configuration NRWTCFG bit, while the wait signal’s polarity is set by the
NRWTPOL bit.
In NOR Flash synchronous burst access mode, when NRWTEN bit in EXMC_SNCTLx
register is set, EXMC_NWAIT signal will be detected af ter a period o f data latency. If
EXMC_NWAIT signal detected is valid, wait cycles will be inserted until EXMC_NWAIT
becomes invalid.
◼
The valid polarity of EXMC_NWAIT:
NRWTPOL= 1: valid level of EXMC_NWAIT signal is high.
NRWTPOL= 0: valid level of EXMC_NWAIT signal is low.
◼
In synchronous burst mode, EXMC_NWAIT signal has two kinds of configurations:
NRWTCFG = 1: When EXMC_NWAIT signal is active, current cycle data is not valid.
NRWTCFG = 0: When EXMC_NWAIT signal is active, the next cycle data is not valid. It is
the def ault state after reset.
During wait-state inserted via the EXMC_NWAIT signal, the controller continues to send clock
pulses to the memory, keep the chip select and output signals availably, and ignore the invalid
data signal.
3. Automatic burst split at CRAM page boundary
Crossing page boundary burst access is prohibited in CRAM 1.5, an automatic burst split
f unctionality is implemented by the EXMC. To guarantee correct burst split operation, users
should specify CRAM page size by conf iguring the CPS bit in EX MC_SNCTLx register to
inf orm the EXMC when this functionality should be performed.
4. Mode SM - Single burst transmission
For synchronous burst transmission, if the needed data of AHB is 16-bit, EXMC will perform