L9803 datasheet(111/126 Pages) STMICROELECTRONICS

111 / 126 page

L9803

Instruction Set

111/126

The relative addressing mode consists of two sub-modes:

Relative (direct):

The offset is following the opcode.

Relative (indirect):

The offset is defined in memory, which address follows the opcode.

6.2

Instruction groups

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 opcodes.

In order to extend the number of available opcodes for an 8-bit CPU (256 opcodes), three

different probate pockets are defined. These prebytes modify the meaning of the instruction

they precede.

The whole instruction becomes:

PC-2

End of previous instruction

PC-1

Prebyte

opcode

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:

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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