LH79524/LH79525 User’s Guide External Memory Controller
Version 1.0 7-43
7.5.2.14 Dynamic Memory Auto-Refresh Period, and Auto-Refresh to
Active Command Period Register (DYNAUTO)
The Dynamic Memory Auto-Refresh Period, and Auto-Refresh to Active Command Period
Register enables programming the Auto-refresh Period, and Auto-refresh to Active Com-
mand Period, tRFC. This value is normally found in SDRAM data sheets as tRFC or some-
times as tRC.
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 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
(DYNMCTRL:SR = 1) prior to entering Disable.
Table 7-37. DYNAUTO 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 /// tRFC
RESET 0000000000011111
TYPE RO RO RO RO RO RO RO RO RO RO RO RW RW RW RW RW
ADDR 0xFFFF1000 + 0x04C
Table 7-38. DYNAUTO Fields
BITS NAME FUNCTION
31:5 /// Reserved Reading returns 0. Write the reset value.
4:0 tRFC
Auto-Refresh Period and Auto-Refresh to Active Command Period
0x00 to 0x1F = (n + 1) External Memory Clock periods
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