參數(shù)資料
型號(hào)： DP8440
文件頁(yè)數(shù)： 20/46頁(yè)
文件大?。?/td> 644K
代理商： DP8440
6.0 Refresh Modes
The DP8440/41 support auto-internal refresh, and external-
ly control refresh. The DP8440/41 arbitrates between re-
freshes and accesses and guarantees precharge timings af-
ter every access and refresh. The DRAM controller will nev-
er interrupt an access in progress to do a refresh, nor will it
interrupt a refresh in progress when an access is requested.
After every refresh the DRAM controller will guarantee the
programmed precharge time before RAS can assert for a
new access or for a second refresh. The refresh period can
be programmed for 15
m
s or for 120
m
s.
6.1 AUTO-INTERNAL REFRESH
This refresh scheme is completely transparent to the CPU.
The DP8440/41 will refresh the DRAM every 15
m
s or
120
m
s, depending on the programming selection. When the
refresh counter expires (every 15
m
s or 120
m
s) the RFRQ
output asserts. On the next rising edge of clock RFIP as-
serts and, one clock period later, RASs assert. RFIP ne-
gates on the same clock edge that RASs negate. If the user
is doing long page or burst accesses, the DP8440/41 will
keep track of up to 6 missed refreshes. At the end of the
access the DRAM controller will burst refresh the locations
missed during the access.
TL/F/11718–10
FIGURE 14. Autointernal Refresh (2T of RAS Low and Precharge)
20
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