Sharp LH79524 - Dynamic Memory Self-Refresh Exit Time Register (REFEXIT); Table 7-27. REFEXIT Register; Table 7-28. REFEXIT Fields

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 0000000000000000
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 0000000000001111
TYPE RO RO RO RO RO RO RO RO RO RO RO RO RW RW RW RW
ADDR 0xFFFF1000 + 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