LH79524/LH79525 User’s Guide
External Memory Controller
Version 1.0
7-51
7.5.2.20 Dynamic Memory RAS and CAS Delay Register for
nDCS0 and nDCS1 (DYNRASCASx)
The Dynamic Memory RAS and CAS Delay Register selects the RAS and CAS latencies
for the relevant dynamic memory. Note that the same value must be programmed into the
device’s Mode register.
These registers must 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
(DYNMCTRL:SR = 1) prior to entering Disable.
NOTE: *The RAS to CAS latency (RAS) and CAS latency (CAS) are both defined in HCLK clock cycles.
Table 7-50. DYNRASCASx 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
///
CAS
///
RAS
RESET
0
0
0
0
0
0
1
1
0
0
0
0
0
0
1
1
TYPE
RO
RO
RO
RO
RO
RO
RW
RW
RW
RW
RW
RW
RW
RW
RW
RW
ADDR
0xFF 0x104 for DYNRASCAS0
0xFF 0x124 for DYNRASCAS1
Table 7-51. DYNRASCASx Fields
BITS
NAME
FUNCTION
31:10
///
Reserved
Reading returns 0. Write the reset value.
9:8
CAS*
CAS Latency
00 = reserved
01 = one clock cycle
10 = two clock cycles
11 = three clock cycles
7:2
///
Reserved
Reading returns 0. Write the reset value.
1:0
RAS*
RAS Latency
00 = reserved
01 = one clock cycle
10 = two clock cycles
11 = three clock cycles