STC89LE53RC datasheet(164/165 Pages) STC

No. de pieza	STC89LE53RC

Descripción Electrónicos	Enhanced 80C51 Central Processing Unit ,6T or 12T per machine cycle

PDF	165 Pages

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Fabricante Electrónico	STC [STCmicro Technology Co,.Ltd]

Página de inicio	http://www.stcmicro.com/

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Registers used in parameter passing

Number of Argument Char / 1-Byte Pointer INT / 2-Byte Pointer Long/Float

Generic Pointer

R6 & R7

R4–R7

R1–R3

R4 &R5

R4–R7

R2 & R3

Since there are only eight registers in the 8051, there may be situations where we do not have enough regist-

ers for parameter passing. When this happens, the remaining parameters can be passed through fixed memory

loacations. To specify that all parameters will be passed via memory, the NOREGPARMs control directive is

used. To specify the reverse, use the REGPARMs control directive.

Return Values

Unlike parameters, which can be passed by using either registers or memory locations, output values must be

returned from functions via registers. The following table shows the registers used in returning different types of

values from functions.

Registers used in returning values from functions

Return Type

Description

bit

Carry Flag (C)

char/unsigned char/1-byte pointer R7

int/unsigned int/2-byte pointer

R6 & R7

MSB in R6, LSB in R7

long/unsigned long

R4–R7

MSB in R4, LSB in R7

float

R4–R7

32-bit IEEE format

generic pointer

R1–R3

Memory type in R3, MSB in R2, LSB in R1

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