ST STM32F412 Reference Manual page 283

RM0402
Bits 19:16 BUSTURN[3:0]: Bus turnaround phase duration
These bits are written by software to add a delay at the end of a write-to-read (and read-to-
write) transaction. This delay allows to match the minimum time between consecutive
transactions (tEHEL from NEx high to NEx low) and the maximum time needed by the
memory to free the data bus after a read access (tEHQZ). The programmed bus turnaround
delay is inserted between an asynchronous read (muxed or mode D) or write transaction and
any other asynchronous /synchronous read or write to or from a static bank. The bank can be
the same or different in case of read, in case of write the bank can be different except for
muxed or mode D.
In some cases, whatever the programmed BUSTURN values, the bus turnaround delay is
fixed
as follows:
• The bus turnaround delay is not inserted between two consecutive asynchronous write
• There is a bus turnaround delay of 1 HCLK clock cycle between:
• There is a bus turnaround delay of 2 HCLK clock cycle between:
• There is a bus turnaround delay of 3 HCLK clock cycle between:
0000: BUSTURN phase duration = 0 HCLK clock cycle added
...
1111: BUSTURN phase duration = 15 x HCLK clock cycles added (default value after reset)
Bits 15:8 DATAST[7:0]: Data-phase duration
These bits are written by software to define the duration of the data phase (refer to
to
0000 0000: Reserved
0000 0001: DATAST phase duration = 1 × HCLK clock cycles
0000 0010: DATAST phase duration = 2 × HCLK clock cycles
...
1111 1111: DATAST phase duration = 255 × HCLK clock cycles (default value after reset)
For each memory type and access mode data-phase duration, refer to the respective figure
(Figure 33
Example: Mode 1, write access, DATAST=1: Data-phase duration= DATAST+1 = 2 HCLK
clock cycles.
Note: In synchronous accesses, this value is don't care.
transfers to the same static memory bank except for muxed mode and mode D.
–Two consecutive asynchronous read transfers to the same static memory bank except for
muxed mode and mode D.
–An asynchronous read to an asynchronous or synchronous write to any static bank or
dynamic bank except for muxed mode and mode D.
–An asynchronous (modes 1, 2, A, B or C) read and a read from another static bank.
–Two consecutive synchronous writes (burst or single) to the same bank.
–A synchronous write (burst or single) access and an asynchronous write or read transfer
to or from static memory bank (the bank can be the same or different for the case of
read.
–Two consecutive synchronous reads (burst or single) followed by any
synchronous/asynchronous read or write from/to another static memory bank.
–Two consecutive synchronous writes (burst or single) to different static bank.
–A synchronous write (burst or single) access and a synchronous read from the same or a
different bank.
Figure 45), used in asynchronous accesses:
to Figure 45).
Flexible static memory controller (FSMC)
RM0402 Rev 6
Figure 33
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