Flexible memory controller (FMC) RM0390
320/1328 RM0390 Rev 4
SDRAM Refresh Timer register (FMC_SDRTR)
Address offset:0x154
Reset value: 0x0000 0000
This register sets the refresh rate in number of SDCLK clock cycles between the refresh
cycles by configuring the Refresh Timer Count value.
Example
where 64 ms is the SDRAM refresh period.
The refresh rate must be increased by 20 SDRAM clock cycles (as in the above example) to
obtain a safe margin if an internal refresh request occurs when a read request has been
accepted. It corresponds to a COUNT value of ‘0000111000000’ (448).
This 13-bit field is loaded into a timer which is decremented using the SDRAM clock. This
timer generates a refresh pulse when zero is reached. The COUNT value must be set at
least to 41 SDRAM clock cycles.
Bit 3 CTB2: Command Target Bank 2
This bit indicates whether the command will be issued to SDRAM Bank 2 or not.
0: Command not issued to SDRAM Bank 2
1: Command issued to SDRAM Bank 2
Bits 2:0 MODE[2:0]: Command mode
These bits define the command issued to the SDRAM device.
000: Normal Mode
001: Clock Configuration Enable
010: PALL (“All Bank Precharge”) command
011: Auto-refresh command
100: Load Mode Register
101: Self-refresh command
110: Power-down command
111: Reserved
Note: When a command is issued, at least one Command Target Bank bit ( CTB1 or CTB2) must be
set otherwise the command will be ignored.
Note: If two SDRAM banks are used, the Auto-refresh and PALL command must be issued
simultaneously to the two devices with CTB1 and CTB2 bits set otherwise the command will
be ignored.
Note: If only one SDRAM bank is used and a command is issued with it’s associated CTB bit set, the
other CTB bit of the the unused bank must be kept to 0.
Refresh rate COUNT 1+()SDRAM clock frequency×=
COUNT SDRAM refresh period Number of rows⁄()20–=
Refresh rate 64 ms 8196rows()⁄ 7.81μs==
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