If any two bank pairs are of the same size, but the other pair is empty or has only one
bank populated, then two-way page interleaving is automatically performed in the two
same-size banks. The banks are paired as follows: 0 and 1, 2 and 3, 4 and 5, 6 and 7. In
addition, Banks 1 and 2 are two-way page interleaved in configurations 09H and 0AH,
with noninterleaved page mode in the remaining banks. Thus, the only configurations in
which no interleaving occurs are 00H, 01H, 08H, 0BH, and 18H.
A RAS timeout feature is provided to support DRAMs requiring a 10 microsecond
maximum RAS-active time. If the timeout is enabled, RAS is not allowed to remain low
continuously for more than about 9.5 microsecond. If the timeout is disabled, periodic
refresh cycles limit the maximum possible RAS active time to about 15 microseconds.
SCATsx Memory Address Mapping Modes
The following table summarizes how CPU address bits are mapped into DRAM row
and column address bits and which bits determine bank selection. The ‘‘R’’ bits do not
necessarily map in an exact one-to-one bit order, but the R bits as a group do correspond
to the CPU address bits indicated. ‘‘Page Size’’ refers to the block size accessible by
changing column address bits only.
Table 5-4.
Memory Address Mapping Modes
CPU Address
Bit
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Page
Size
4MW, 2-way
R
R
R
R
R
R
R
R
R
R
R
*
C
C
C
C
C
C
C
C
C
C
C
----
4KB
4MW, Page only
----
R
R
R
R
R
R
R
R
R
R
R
C
C
C
C
C
C
C
C
C
C
C
----
4KB
1MW, 4-way
----
R
R
R
R
R
R
R
R
R
R
*
*
C
C
C
C
C
C
C
C
C
C
----
2KB
1MW, 2-way
----
----
R
R
R
R
R
R
R
R
R
R
*
C
C
C
C
C
C
C
C
C
C
----
2KB
1MW, Page only
----
----
----
R
R
R
R
R
R
R
R
R
R
C
C
C
C
C
C
C
C
C
C
----
2KB
256KW, 4-way
----
----
----
R
R
R
R
R
R
R
R
R
*
*
C
C
C
C
C
C
C
C
C
----
1KB
256KW, 2-way
----
----
----
----
R
R
R
R
R
R
R
R
R
*
C
C
C
C
C
C
C
C
C
----
1KB
256KW,
Page Only
----
----
----
----
----
R
R
R
R
R
R
R
R
R
C
C
C
C
C
C
C
C
C
----
1KB
R
C
*
---- = High level decoding and byte Selection
W = Word (even and odd bytes)
= Row address bit
= Column address bit
= Bank select bit for interleaving
System Interface
DRAM Interface
I
Chips and Technologies, Inc.
P R E L I M I N A R Y
Revision 3.0
5-9