IBM 5150 Hardware Reference Manual page 278

OPERAND SUMMARY
"reg" field Bit Assignments:
16-Bit (w=l) a-Bit (w=O) Segment
000 AX 000 AL 00
ES
001 CX 001 CL
01 CS
010 OX 010
OL
10 SS
011 BX 011 BL
11 OS
100 SP 100 AH
101 BP 101
CH
110 SI
110 OH
111
01 111
BH
SECOND INSTRUCTION BYTE SUMMARY
I
mod
I
xxx
I
rim
I
mod Displacement
00 OISP = 0*, disp-Iow and disp-high are absent
01 OISP
=
disp-Iow sign-extended to 16-bits, disp-high is absent
10 OISP = disp-high: disp-Iow
11
rim
is treated as a "reg" field
rIm
Operand Address
000 (BX) + (SI) + DISP
001 (BX) +
(01)
+ DISP
010 (BP) + (SI) + OISP
011 (BP) +
(01)
+ OISP
100 (SI) + DISP
101
(01)
+ OISP
110 (BP)+OISP*
111 (BX) + OISP
OISP follows 2nd byte of instruction (before data if required).
*except if mod = 00 and
rim
= 110 then EA
=
disp-high: disp-Iow.
B-3