ST7285C datasheet(83/117 Pages) STMICROELECTRONICS

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ST7285C

5.3 ST7 INSTRUCTION SET

The ST7 family devices use an Instruction Set

consisting of 63 instructions. The instructions may

be subdivided into 13 main groups as illustrated in

the following table:

Using a pre-byte

The instructions are described with one to four op-

codes.

In order to extend the number of available op-

codes for an 8-bit CPU (256 op-codes), three dif-

ferent prebyte opcodes are defined. These preb-

ytes modify the meaning of the instruction they

precede.

The whole instruction becomes:

PC-2

End of previous instruction

PC-1

Prebyte

Op-code

PC+1

Additional word (0 to 2) according to the

number of bytes required to compute the

effective address

These prebytes enable instruction in Y as well as

indirect addressing modes to be implemented.

They precede the opcode of the instruction in X or

the instruction using direct addressing mode. The

prebytes are:

PDY 90Replace an X based instruction using im-

mediate, direct, indexed, or inherent ad-

dressing mode by a Y one.

PIX 92 Replace an instruction using direct, direct

bit, or direct relative addressing mode to

an instruction using the corresponding in-

direct addressing mode.

It also changes an instruction using X in-

dexed addressing mode to an instruction

using

indirect

indexed

addressing

mode.

PIY 91 Replace an instruction using X indirect in-

dexed addressing mode by a Y one.

Load and Transfer

CLR

Stack operation

PUSH

POP

RSP

Increment/Decrement

INC

DEC

Compare and Tests

TNZ

BCP

Logical operations

AND

XOR

CPL

NEG

Bit Operation

BSET

BRES

Conditional Bit Test and Branch

BTJT

BTJF

Arithmetic operations

ADC

ADD

SUB

SBC

MUL

Shift and Rotates

SLL

SRL

SRA

RLC

RRC

SWAP

SLA

Unconditional Jump or Call

JRA

JRT

JRF

CALL

CALLR

NOP

RET

Conditional Branch

JRxx

Interruption management

TRAP

WFI

HALT

IRET

Code Condition Flag modification

SIM

RIM

SCF

RCF

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