Jan Yin Chan Electronics Co.,LTD. 386SX Single Chip PC
M6117D : System on a chip
DM&P
Jan Yin Chan Electronics Co,. LTD. M6117D 386SX Single Chip PC Page 27
8F-1,No.22,Wuchyuan 2RD.,Hsin Chuang city Taipei Hsien, Taiwan, R.O.C. Tel: 886-(02) 2298-0770 Fax: (02) 2299-1883
(G) Shadow EF, A[20-23]=1111, or A[20-23] = 0000, Remap type=Move-out remap and memory mode cannot be 10, 19,
21, 22, 25, 28, 29, 30, 31
A19 A18 A17 A16 PA23 PA22 PA21 PA20 PA19 PA18 PA17
1 1 1 x 0 0 0 0 1 1 1
FE0000h
100000h
0E0000h
0C0000h
0A0000h
000000h
15.EF MB
Shadow EF
Page CD
Page AB
Remap 15M.EF to
Page 0M.EF
4.3.6 Shadow Control
The address 0C0000h~ 0FFFFFh is for ROM or unused areas. When the range address is used for ROM, the system can
use RAM to map the area to enhance performance. The address 0C0000~0FFFFFh is also called shadow region. The
shadow region can be read/write control. For example, when it is read enable, write disable, the operation of shadow RAM
is the same as ROM. By programming index 14h, 15h, BIOS programmer can set the read/write control function to initialize
the system. Suppose 0C0000h~0C7FFFh video ROM is present, and 0C0000h~ 0C7FFFh region wants to be shadowed,
then the setup steps are :
(1) Index 14h : D[1-0] = 00, Shadow region 0C0000h ~ 0C7FFFh read/write both disable. Allow the process to be read from
ROM only.
(2) Index 14h : D[1-0] = 10, Shadow region 0C0000h ~ 0C7FFFh read disable, write enable. Allow the process to be read
from ROM and write to DRAM (Shadow RAM). Then video ROM data copies to shadow RAM region.
(3) Index 14h : D[1-0] = 01, Shadow region 0C0000h ~0C7FFFh read enable, write disable. Allow the operation to be read
from DRAM. The video ROM read process is via shadow RAM 0C0000h~ 0C7FFFh region, not via video ROM.
The range of 0C0000h ~ 0FFFFFh partitions to eight blocks, each block is 32KB. Each shadow region block can be shadow
read/write disabled or enabled by programming index 14h, 15h.
The A0000h ~ B0000h region can set to shadow enable. If host read/write this region, the data will read/write from local
memory when enable shadow.
How to set shadow A/B region ?
Index 3ch:
bit 3 = 0, Disable shadow A/B function
bit 3 = 1, Enable shadow A/B function
Index 12h:
bit 1 = 0, Disable shadow A/B region. All access to A/B memory region will pass to ISA
bit 1 = 1, Enable shadow A/B region. All access to A/B memory region will be at local memory.
Only both the index 3ch and 12h enable, the shadow A/B region will enable.
4.3.7 BIOS ROM control
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