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82C836 Datasheet, PDF (47/205 Pages) List of Unclassifed Manufacturers – Single-Chip 386sx AT | |||
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s DRAM Interface
System Interface
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
ICR 4DH Bits 4-0 Â
00H Â
01H
02H Â
03H Â
04H
05H
06H
07H
08H Â
09H Â
0AH Â
0BH
0CH
0DH
0EH Â
0
0
256KW
256KW
256KW
256KW
256KW
256KW
256KW
256KW
256KW
256KW
1MW
1MW
1MW
1MW
1
0
0
256KW
256KW
256KW
256KW
256KW
256KW
1MW
1MW
1MW
0
1MW
1MW
1MW
Banks Â
2
0
0
0
0
256KW
256KW
1MW
1MW
0
1MW
1MW
0
0
1MW
1MW
3
4-7
0
0
0
0
0
0
0
0
0
0
256KW
0
0
0
1MW
0
0
0
0
0
1MW
0
0
0
0
0
0
0
1MW
0
Total Local Memory
0
512KB
1MB
640K + 384K
1.5MB
2MB
3MB
5MB
2.5MB
4.5MB
6.5MB
2MB
4MB
6MB
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 M exists.
 The DRAM is mapped as 1MB conventional (subject to enabling or disabling of the top 384K) and no ext ended memory.
 The DRAM is mapped as 640KB conventional, 384KB extended. The 384KB block is addressed at 100000H-1 5FFFFH. There is no shadow RAM.
 In all configurations, all memory beyond the first 1MB (or beyond the first 640KB in configuration 0 3H) is available for use as extended memory (addressed
linearly starting at 100000H). Extended memory can be accessed either directly (in 80386sx protecte d mode) or through expanded memory address translation
(EMS).
 Banks are normally mapped in ascending physical address order i.e., Bank 1 has a higher starting add ress than Bank 0, etc. However, in configuration 08-0AH,
the mapping order is changed so that the 256KW bank has the highest starting address instead of the lowest.
5-6 Revision 3.0
PRELIMINARY
Chips and Technologies, Inc.
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