LH79524/LH79525 User’s Guide
External Memory Controller
Version 1.0
7-37
7.5.2.8 Dynamic Memory Active to Precharge Command Period
Register (DYNM2PRE)
The Dynamic Memory Active to Precharge Command Period Register enables program-
ming the Active to Precharge Command Period, tRAS. This value is normally found in
SDRAM data sheets as t
RAS
.
This register should only be modified during system initialization, or when there are
no current or outstanding transactions. Software can ensure that there are no current or
outstanding transactions by waiting until the memory controller is idle, then entering Low-
Power Mode (CONTROL:MODE = 1), or Disable Mode (CONTROL:ENABLE = 0). When
in these two modes, external memory access is not allowed, ensuring that changing
parameters will not corrupt external data. Low-Power Mode automatically refreshes
SDRAM; Disable Mode requires commanding the SDRAM to Self Refresh (DYNMC-
TRL:SR = 1) prior to entering Disable.
Table 7-25. DYNM2PRE Register
BIT
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
FIELD
///
RESET
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
TYPE
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
BIT
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
FIELD
///
tRAS
RESET
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
TYPE
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RW
RW
RW
RW
ADDR
0xFF 0x034
Table 7-26. DYNM2PRE Fields
BITS NAME
FUNCTION
31:4
///
Reserved
Reading returns 0. Write the reset value.
3:0
tRAS
Active to Precharge Command Period
Period = (tRAS + 1) External Memory Clock periods