DP8430V datasheet(23/56 Pages) NSC

23 / 56 page

50 Refresh Options (Continued)

52 REFRESH CYCLE TYPES

Three different types of refresh cycles are available for use

The three different types are mutually exclusive and can be

used with any of the three modes of refresh control The

three different refresh cycle types are all RAS refresh stag-

gered RAS refresh and error scrubbing during all RAS re-

fresh In all refresh cycle types the RAS precharge time is

guaranteed between the previous access RAS ending and

the refresh RAS0 starting between refresh RAS3 ending

and access RAS beginning between burst refresh RASs

521 Conventional RAS Refresh

A conventional refresh cycle causes RAS0 – 3 to all assert

from the first positive edge of CLK after RFIP is asserted as

shown in

Figure 16 RAS0 – 3 will stay asserted until the

number of positive edges of CLK programmed have passed

On the last positive edge RAS0 – 3 and RFIP will be negat-

ed This type of refresh cycle is programmed by negating

address bit R9 during programming

TLF11118 – 25

FIGURE 16 Conventional RAS Refresh

522 Staggered RAS Refresh

A staggered refresh staggers each RAS or group of RASs

by a positive edge of CLK as shown in

Figure 17 The num-

ber of RASs which will be asserted on each positive edge

of CLK is determined by the RAS CAS configuration mode

programming bits C4 – C6 If single RAS outputs are select-

ed during programming then each RAS will assert on suc-

cessive positive edges of CLK If two RAS outputs are se-

lected during programming then RAS0 and RAS1 will assert

on the first positive edge of CLK after RFIP is asserted

RAS2 and RAS3 will assert on the second positive edge of

CLK after RFIP is asserted If all RAS outputs were selected

during programming all RAS outputs would assert on the

first positive edge of CLK after RFIP is asserted Each RAS

or group of RASs will meet the programmed RAS low time

and then negate

TLF11118 – 26

FIGURE 17 Staggered RAS Refresh

DP8430V датащи(PDF) 23 Page - National Semiconductor (TI)