External Memory Controller
LH79524/LH79525 User’s Guide
7-38
Version 1.0
7.5.2.9 Dynamic Memory Self-Refresh Exit Time Register (REFEXIT)
The Dynamic Memory Self-Refresh Exit Time Register enables programming the
Self-refresh Exit Time, tSREX. This value is normally found in SDRAM data sheets as
t
SREX
. This register is used as the self-refresh exit time for all chip selects. Therefore, it
must be programmed with the longest exit time period required of all the chip selects.
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 out-
standing 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 7-27. REFEXIT 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
///
tSREX
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 0x038
Table 7-28. REFEXIT Fields
BITS NAME
FUNCTION
31:4
///
Reserved
Reading returns 0. Write the reset value.
3:0
tSREX
Self-Refresh Exit Time
Exit Time = (tSREX + 1) External Memory Clock periods