OVERVIEW OF THE 80C186 FAMILY ARCHITECTURE

2.2.1.6Processor Control Instructions

Processor control instructions (see Table 2-11) allow programs to control various CPU functions. Seven of these instructions update flags, four of them are used to synchronize the microprocessor with external events, and the remaining instruction causes the CPU to do nothing. Except for flag operations, processor control instructions do not affect the flags.

Table 2-11. Processor Control Instructions

 

Flag Operations

 

 

STC

Set Carry flag

CLC

Clear Carry flag

CMC

Complement Carry flag

STD

Set Direction flag

CLD

Clear Direction flag

STI

Set Interrupt Enable flag

CLI

Clear Interrupt Enable flag

 

 

 

External Synchronization

 

 

HLT

Halt until interrupt or reset

WAIT

Wait for

 

pin active

TEST

ESC

Escape to external processor

LOCK

Lock bus during next instruction

 

 

 

No Operation

 

 

NOP

No operation

 

 

 

 

2.2.2Addressing Modes

The 80C186 Modular Core family members access instruction operands in several ways. Oper- ands can be contained either in registers, in the instruction itself, in memory or at I/O ports. Ad- dresses of memory and I/O port operands can be calculated in many ways. These addressing modes greatly extend the flexibility and convenience of the instruction set. The following para- graphs briefly describe register and immediate modes of operand addressing. A detailed descrip- tion of the memory and I/O addressing modes is also provided.

2.2.2.1Register and Immediate Operand Addressing Modes

Usually, the fastest, most compact operand addressing forms specify only register operands. This is because the register operand addresses are encoded in instructions in just a few bits and no bus cycles are run (the operation occurs within the CPU). Registers can serve as source operands, des- tination operands, or both.

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Intel 80C188XL, 80C186XL user manual Processor Control Instructions, Register and Immediate Operand Addressing Modes