Intel 210200-002 manual Data Registers Pointer and Index Registers

ARCHITECTURE AND INSTRUCTIONS

In certain instances, specific uses of these four registers are indicated by the mnemonic phrases "stack pointer," "base pointer," "source index," and "destination index." (Fig. 2-2).

Segment Register File

The segment registers of the 8088 are 16-bit registers. These registers specifically identify the four currently addressable memory seg- ments: CS (code segment), DS (data segment),

SS(stack segment), and ES (extra segment). All instructions are fetched from the current

code segment offset by the instruction pointer (IP) register. The segment for operand fetches can usually be designated by append- ing a special one-byte prefix to the instruc- tion. This prefix, and other prefixes described later, has unique encoding that distinguishes it from the opcodes. In the absence of such a prefix (the usual case), the operand is usually fetched from the current data segment or cur- rent stack segment, depending on whether the offset address was calculated from the contents of a pointer register.

DATA REGISTERS

7	07	o
AX	AH	AL
BX	BH	BL
CX	CH	CL
OX	DH	DL

POINTER AND INDEX REGISTERS

	15	0
SP			STACK POINTER
BP			BASE POINTER
SI	I	I	SOURCE INDEX
DI			DESTINATION INDEX
		SEGMENT REGISTERS
	15	0
CS			CODE
OS			DATA
SS	I	I	STACK
ES			EXTRA
		INSTRUCTION POINTER AND FLAGS
	15	0	INSTRUCTION
IP	I	lolDlllTlslzl IA I I pi lei
			POINTER
FLAGS

1511 10 9 8 7 6 5 4 3 2 1 0

Figure 2-2. 8088 Register Structure

2-3