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Character Map Select Register Format
Bit
7
6
5
4
3
2
1
0
1 1 1 1
'
~
I
I
~I
: : :
Character Map Select B
-
-
Character Map Select A
'--""---'---.........
---------l~
Not Used
Bit O-Bit 1
Bits
1
0
Value
0
0
0
1
1
0
1
1
Bit 2-Bit 3
Bits
3
2
Value
0
0
0
1
1
0
1
1
Character Map Select B-Selects the map used
to generate alpha characters when attribute bit 3
is a 0, according to the following table:
Map
Selected
Table Location
0
1 st 8K of Plane 2 Bank 0
1
2nd 8K of Plane 2 Bank 1
2
3rd 8K of Plane 2 Bank 2
3
4th 8K of Plane 2 Bank 3
Character Map Select A-Selects the map used
to generate alpha characters when attribute bit 3
is a 1, according to the following table:
Map
Selected
Table Location
0
1 st 8K of Plane 2 Bank 0
1
2nd 8K of Plane 2 Bank 1
2
3rd 8K of Plane 2 Bank 2
3
4th 8K of Plane 2 Bank 3
In alphanumeric modes, bit 3 of the attribute byte normally has
the function of turning the foreground intensity on or off. This
bit however may be redefined as a switch between character sets.
This function is enabled when there is a difference between the
value in Character Map Select A and the value in Character Map
Select B. Whenever these two values are the same, the character
select function is disabled. The memory mode register bit 1 must
be a 1 (indicates the memory extension card is installed in the
unit) to enable this function; otherwise, bank 0 is always selected.
22 IBM Enhanced Graphics Adapter
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