In addition to the memory address ranges for ROM and shadow RAM discussed
earlier, local RAM can be enabled or disabled in a single 384KB block in the range
040000H-09FFFFH (ICR 4EH). Memory addresses in the range 100000H-FFFFFFH
(extended memory) and EMS access (expanded memory) are discussed in a later section
titled
SCATsx Memory Bank Utilization
. Memory accesses always go to the AT bus,
unless local RAM or ROM has been enabled at the referenced memory address.
Bits 4-0 of internal configuration register 4DH must be set according to the physical
DRAM configuration. Table 5-1 shows the valid configurations with either nonencoded
RAS or encoded RAS. Table 5-2 shows additional configurations that are valid only
with encoded RAS. Table 5-3 shows the 4MB configurations, valid only with
nonencoded RAS.
Table 5-1.
Valid Configurations----Nonencoded or Encoded RAS
Banks
ICR 4DH Bits 4-0
0
1
2
3
4-7
Total Local Memory
00H
0
0
0
0
0
0
01H
02H
03H
256KW
0
0
0
0
512KB
256KW
256KW
0
0
0
1MB
256KW
256KW
0
0
0
640K + 384K
04H
256KW
256KW
256KW
0
0
1.5MB
05H
256KW
256KW
256KW
256KW
0
2MB
06H
256KW
256KW
1MW
0
0
3MB
07H
08H
09H
0AH
256KW
256KW
1MW
1MW
0
5MB
256KW
1MW
0
0
0
2.5MB
256KW
1MW
1MW
0
0
4.5MB
256KW
1MW
1MW
1MW
0
6.5MB
0BH
1MW
0
0
0
0
2MB
0CH
1MW
1MW
0
0
0
4MB
0DH
0EH
1MW
1MW
1MW
0
0
6MB
1MW
1MW
1MW
1MW
0
8MB
K = 1024 M = 1048576 W = word (two bytes) B = byte
All memory accesses go to the AT bus. This can be used to turn off on-board RAM even if on-board RA
The DRAM is mapped as 1MB conventional (subject to enabling or disabling of the top 384K) and no ext
The DRAM is mapped as 640KB conventional, 384KB extended. The 384KB block is addressed at 100000H-1
In all configurations, all memory beyond the first 1MB (or beyond the first 640KB in configuration 0
linearly starting at 100000H). Extended memory can be accessed either directly (in 80386sx protecte
(EMS).
Banks are normally mapped in ascending physical address order i.e., Bank 1 has a higher starting add
the mapping order is changed so that the 256KW bank has the highest starting address instead of the
M exists.
ended memory.
5FFFFH. There is no shadow RAM.
3H) is available for use as extended memory (addressed
d mode) or through expanded memory address translation
ress than Bank 0, etc. However, in configuration 08-0AH,
lowest.
I
DRAM Interface
System Interface
5-6
Revision 3.0
P R E L I M I N A R Y
Chips and Technologies, Inc.