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CHAPTER 12 EXTERNAL BUS INTERFACE
12.2.1
External Bus Mode registers (EBM)
The External Bus Mode register defines the bus mode of the external bus interface. For
the External Boot Vector fetch, the external bus mode byte is read externally from the
address FFFFDF
and written to the register directly after reading the Boot Vector.
H
Following settings can be done in the EBM register:
- activation of all external bus areas
- switching between internal ROM access and external access
- multiplexed/non-multiplexed external bus access mode
■ External Bus Mode register
7
Address:
0006F0
NMS
ERE
H
R/W R/W R/W R/W R/W
R/W
: Readable and writable
: Initial value (in internal vector mode)
* initial values
1 1 1 0 0 0 0 0
after external Boot Vector fetch, MD[2:0] = 110 (except MB96(F)38x at external Boot Vector fetch in non-multiplexed bus mode)
B
1 1 0 1 0 0 0 0
after external Boot Vector fetch, MD[2:0] = 110 (MB96(F)38x at external Boot Vector fetch in non-multiplexed bus mode only)
B
0 1 1 0 0 0 0 0
after external Boot Vector fetch, MD[2:0] <> 110
B
302
Figure 12.2-4 External Bus Mode register (EBM)
6
5
4
3
2
1
0
EAE2 EAE1 EAE0
EAE5 EAE4 EAE3
R/W R/W R/W
MB96300 Super Series Hardware Manual
Initial value
0 0 0 0 0 0 0 0
*
B
bit5-bit0
EAE[5-0]
External area enable
0
Corresponding external area is disabled
1
Corresponding external area is enabled
bit6
ERE
External ROM enable
0
External ROM is disabled (internal ROM enabled)
1
External ROM is enabled (external area must be enabled)
bit7
NMS
Non-multiplexed bus select
0
Address/Data multiplexed
1
Address/Data non-multiplexed
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