IBM RT Series Hardware Reference Manual page 346

TNL SN20-9844 (March 1987) to 75X0235
Branch Command
I/O DATA FIELD
71
8
I I I I I
I
I
Figure 22. Branch Command Word
Bits 00-02 BRANCH DECODE
( 1 1 1 )
Bit 00-15 BRANCH (Absolute) ADDRESS FIELD (16 bits)
The branch address is 16 bits. The 10 high order bits (including the 3 branch decode bits) of the
branch command word correspond to a Y address.
Y ADDRESS (10 bits) X ADDRESS (10 bits)
I I I
1
0
1
0
1
0
1
0
I
16 Bits
Branch Command Word
~
Figure 23. Branch Command Word Address Field
The other 6 (low order) bits of the branch command word form the most significant 6 bits of a
10-bit X address with the 4-least significant bits assumed to be all O's. Therefore, branching is
restricted to 16-bit word boundaries (4 LSB's of X address are all O's) and the lower 1/8 of the
bit map (Y address greater than or equal X'380', scan lines 896-1023).
34 Extended Monochrome Graphics Adapter