![Freescale Semiconductor MCF54455 Reference Manual Download Page 512](http://html1.mh-extra.com/html/freescale-semiconductor/mcf54455/mcf54455_reference-manual_2330541512.webp)
SDRAM Controller (SDRAMC)
Freescale Semiconductor
21-25
21.5.1.7
Auto-Refresh Command (REF)
The memory controller issues auto-refresh commands according to the SDCR[REF_CNT] value. Each
time the programmed refresh interval elapses, the memory controller issues a
PALL
command followed by
a REF command.
If a memory access is in progress at the time the refresh interval elapses, the memory controller schedules
the refresh after the transfer finishes; the interval timer continues counting so the average refresh rate is
constant.
After REF command, the SDRAM is in an idle state and waits for an
ACTV
command.
21.5.1.8
Self-Refresh (SREF) and Power Down (PDWN) Commands
The memory controller issues a PDWN or a SREF command if the SDCR[CKE] bit is cleared. If the
SDCR[REF_EN] bit is set when CKE is negated, the controller issues a SREF command; if the REF_EN
bit is cleared, the controller issues a PDWN command. The REF_EN bit may be changed in the same
register write that changes the CKE bit; the controller acts upon the new value of the REF_EN bit.
Like an auto-refresh command, the controller automatically issues a
PALL
command before the self-refresh
command.
The memory reactivates from power-down or self-refresh mode by setting the CKE bit.
If a normal refresh interval elapses while the memory is in self-refresh mode, a PALL and REF performs
when the memory reactivates. If the memory is put into and brought out of self-refresh all within a
single-refresh interval, the next automatic refresh occurs on schedule.
In self-refresh mode, memory does not require an external clock. The SD_CLK can be stopped for
maximum power savings. If the memory controller clock is stopped, the refresh-interval timer must be
reset before the memory is reactivated (if periodic refresh is to be resumed). The refresh-interval timer
resets by clearing the REF_EN bit. This can be done at any time while the memory is in self-refresh mode,
before or after the memory controller clock is stopped/restarted, but
not
with the same control register
write that clears CKE; this would put the memory in power down mode. To restart periodic refresh when
the memory reactivates, the REF_EN bit must be reasserted; this can be done before the memory
reactivates or in the same control register write that sets CKE to exit self-refresh mode.
BA1
BA0
A12
A11
A10
A9
A8
A7
A6
A5
A4
A3
A2
A1
A0
Field
1
1
0
Figure 21-15. DDR2 Extended Mode Register 3
Table 21-17. DDR2 Extended Mode Register 2 and 3 Field Descriptions
Field
Description
BA1–BA0
Bank Address. BA1 must be set to 1. To select DDR2 extended mode register 2, BA0 has to be a 0. To
select DDR2 extended mode register 3, BA0 has to be a 1.
A12–A0
Reserved for future use. All bits except for BA1 and BA0 must be programmed to 0 when setting the mode
register during initialization.
Summary of Contents for MCF54455
Page 33: ...xxviii Freescale Semiconductor ...
Page 67: ...Freescale Semiconductor 1 ...
Page 125: ...Freescale Semiconductor 1 ...
Page 145: ...Enhanced Multiply Accumulate Unit EMAC 5 21 Freescale Semiconductor ...
Page 173: ...Cache 6 28 Freescale Semiconductor ...
Page 179: ...Static RAM SRAM 7 6 Freescale Semiconductor ...
Page 207: ...Power Management 9 16 Freescale Semiconductor ...
Page 323: ...Reset Controller Module 13 8 Freescale Semiconductor ...
Page 389: ...Pin Multiplexing and Control 16 44 Freescale Semiconductor ...
Page 575: ...PCI Bus Controller 22 58 Freescale Semiconductor ...
Page 600: ...Advanced Technology Attachment ATA Freescale Semiconductor 23 25 ...
Page 601: ...Freescale Semiconductor 1 ...
Page 842: ...I2 C Interface Freescale Semiconductor 33 16 ...
Page 843: ...Freescale Semiconductor 1 ...
Page 921: ...Revision History A 6 Freescale Semiconductor ...