6-28 Intel® PXA255 Processor Developer’s Manual

Memory Controller

The programmable opcode for address bits MA<24:17> used during the mode-register set

command (MRS) is exactly what is programmed in the MDMRS register.

6.5.7 SDRAM Waveforms

Normal operation of the SDRAM controller is shown in Figure6-5 through Figure 6-11.

Table 6-11. SDRAM Command Encoding

Command
Pins
SDCKE
(at clk
n-1)
SDCKE
(at clk
n)
nSDCS
3:0 nSDRAS nSDCAS nWE DQM
3:0
MA <24:10>
24:23 22:21 20 19:10
PWRDN 101 1 111 x
PWRDNX 011 1 111 x
SLFRSH 100 0 010 x
CBR 1100 01x x
MRS 1 x 0 0 0 0 0 OP code
ACT 1x00 11xbank row
READ 1 x 0 1 0 1 0 bank col 0 col
WRITE 1 x 0 1 0 0 mask bank col 0 col
PALL
PRE
All 1x00 10x
xx1x
Bank bank 0
NOP 1x1xxx
xx
0111

Table 6-12. SDRAM Mode Register Opcode Table

Address Bits Option Value
MA<24:17> reserved MDMRSx
MA[16:14] CAS Latency = 2 010
CAS Latency = 3 011
MA[13] Sequential Burst 0
MA[12:10] Burst Length = 4 010