ST STM32L4+ Series Reference Manual page 507

RM0432
18.7.4 NOR Flash/PSRAM controller asynchronous transactions
Asynchronous static memories (NOR Flash, PSRAM, SRAM, FRAM)
• Signals are synchronized by the internal clock HCLK. This clock is not issued to the
memory
•
The FMC always samples the data before de-asserting the NOE signal. This
guarantees that the memory data hold timing constraint is met (minimum Chip Enable
high to data transition is usually 0 ns)
•
If the Extended mode is enabled (EXTMOD bit is set in the FMC_BCRx register), up to
four extended modes (A, B, C and D) are available. It is possible to mix A, B, C and D
modes for read and write operations. For example, read operation can be performed in
mode A and write in mode B.
•
If the Extended mode is disabled (EXTMOD bit is reset in the FMC_BCRx register), the
FMC can operate in mode 1 or mode 2 as follows:
–
–
Mode 1 - SRAM/FRAM/PSRAM (CRAM)
The next figures show the read and write transactions for the supported modes followed by
the required configuration of FMC_BCRx, and FMC_BTRx/FMC_BWTRx registers.
A[25:0]
NBL[x:0]
NEx
NOE
NWE
Data bus
Mode 1 is the default mode when SRAM/PSRAM memory type is selected (MTYP
= 0x0 or 0x01 in the FMC_BCRx register)
Mode 2 is the default mode when NOR memory type is selected (MTYP = 0x10 in
the FMC_BCRx register).
Figure 48. Mode 1 read access waveforms
High
NBLSET ADDSET HCLK cycles
HCLK
cycles
Flexible static memory controller (FSMC)
Memory transaction
DATAST HCLK cycles
RM0432 Rev 6
Data driven by memory
DATAHLD
HCLK cycles
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