LH79524/LH79525 User’s Guide
External Memory Controller
Version 1.0
7-55
7.5.2.23 Static Memory Output Enable Delay Registers (SWAITOENx)
The Static Memory Output Enable Delay Registers enable programming the delay from the
Valid Address to nOE assertion. See Section 7.2.4.1.1 for a complete description of pro-
gramming these registers.
The total Read cycle time is the total time that the address is valid. During this time, several
parameters are programmable. In the following equations, ‘D’ represents the SWAITOENx
register, ‘E’ represents the SWAITRDx register, and ‘C’ represents the address hold time.
In general, Read wait states can be derived from the following equation:
tRC (Read cycle time) = tD1 + tD2 + ... tDn + tE0 + tE1 + ... tEn + C, where the length of
each term is one HCLK period, and ‘n’ is the value programmed in the respective register.
The minimum value for the equation is tRC = tE0 + C, and is therefore the zero wait
state timing.
Thus, Read wait states can be programmed using the appropriate mix of nOE extension
(programmed in SWAITRDx) with nOE assertion delay (programmed in SWAITOENx).
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.
Table 7-56. SWAITOENx 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
///
WAITOEN
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
RW
RW
RW
RW
ADDR
0xFF 0x208 for SWAITOEN0
0xFF 0x228 for SWAITOEN1
0xFF 0x248 for SWAITOEN2
0xFF 0x268 for SWAITOEN3
Table 7-57. SWAITOENx Fields
BITS
NAME
FUNCTION
31:4
///
Reserved
Reading returns 0. Write the reset value.
3:0
WAITOEN
Wait Output Enable
Delay from Valid Address to assertion of nOE. See
Section 7.2.4.1.1 for timing examples.