Motorola ColdFire MCF5281 - Manual (Page 287)

Synchronous DRAM Controller Module
Freescale Semiconductor 15-15
Figure 15-7. Burst Write SDRAM Access
Accesses in synchronous burst page mode always cause the following sequence:
1. ACTV command
2. NOP commands to assure SRAS-to-SCAS delay (if CAS latency is 1, there are no NOP
commands).
3. Required number of READ or WRITE commands to service the transfer size with the given port
size.
4. Some transfers need more NOP commands to assure the ACTV -to-precharge delay.
5. PALL command
6. Required number of idle clocks inserted to assure precharge-to- ACTV delay.
15.2.3.5 Auto-Refresh Operation
The DRAM controller is equipped with a refresh counter and control. This logic is responsible for
providing timing and control to refresh the SDRAM without user interaction. Once the refresh counter is
set, and refresh is enabled, the counter counts to zero. At this time, an internal refresh request flag is set
and the counter begins counting down again. The DRAM controller completes any active burst operation
and then performs a
PALL operation. The DRAM controller then initiates a refresh cycle and clears the
refresh request flag. This refresh cycle includes a delay from any precharge to the auto-refresh command,
the auto-refresh command, and then a delay until any
ACTV command is allowed. Any SDRAM access
initiated during the auto-refresh cycle is delayed until the cycle is completed.
A[23:0]
SRAS
SCAS
DRAMW
D[31:0]
ACTV WRITE PALL NOP
SDRAM_CS[0] or [1]
BS[3:0]
t
CASL
= 2
Row Column Column Column Column
t
RP
t
RWL
CLKOUT
NOP WRITE WRITE WRITE
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3