INSTRUCTION SET REFERENCE

Operation:

DJNZ

 

(PC) ← (PC) + 2

 

(Rn) ← (Rn) – 1

 

IF (Rn) > 0 or (Rn) < 0

 

THEN

 

(PC) ← (PC) + rel

 

 

ECALL <dest>

 

Function:

Extended call

Description:

Calls a subroutine located at the specified address. The instruction adds four to the program

 

counter to generate the address of the next instruction and then pushes the 24-bit result

 

onto the stack (high byte first), incrementing the stack pointer by three. The 8 bits of the high

 

word and the 16 bits of the low word of the PC are then loaded, respectively, with the

 

second, third and fourth bytes of the ECALL instruction. Program execution continues with

 

the instruction at this address. The subroutine may therefore begin anywhere in the full 16-

 

Mbyte memory space.

Flags:

CY

AC

OV

N

Z

 

 

 

 

 

—

—

—

—

—

 

 

 

 

 

Example: The stack pointer contains 07H and the label “SUBRTN” is assigned to program memory location 123456H. After executing the instruction

ECALL SUBRTN

at location 012345H, SP contains 0AH; on-chip RAM locations 08H, 09H and 0AH contain 01H, 23H and 45H, respectively; and the PC contains 123456H.

Variations

ECALL addr24

Binary Mode Source Mode

Bytes:

5

 

4

 

States:

14

 

13

[Encoding]

 

 

 

 

1 0 0 1

 

1 0 1 0

 

 

 

 

 

Hex Code in:

Binary Mode = [A5][Encoding]

 

Source Mode = [Encoding]

Operation:

ECALL

 

 

 

(PC) ← (PC) + 4

 

 

(SP) ← (SP) + 1 ((SP)) ← (PC.23:16) (SP) ← (SP) + 1 ((SP)) ← (PC.15:8) (SP) ← (SP) + 1 ((SP)) ← (PC.7:0) (PC) ← (addr.23:0)

addr23–

addr16

addr15–addr8

addr7–addr0

A-59

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Intel 8XC251SP, 8XC251SA, 8XC251SQ, 8XC251SB, Embedded Microcontroller manual Ecall dest Function, Ecall Subrtn
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Embedded Microcontroller, 8XC251SP, 8XC251SA, 8XC251SQ, 8XC251SB specifications

The Intel 8XC251 series of embedded microcontrollers is a family of versatile and powerful devices, designed to meet the demands of a wide range of applications. With models such as the 8XC251SB, 8XC251SQ, 8XC251SA, and 8XC251SP, this series offers unique features while maintaining a high level of performance and reliability.

At the heart of the 8XC251 microcontrollers is the 8051 architecture, which provides a 16-bit processor capable of executing complex instructions efficiently. This architecture not only allows for a rich instruction set but also facilitates programming in assembly language and higher-level languages like C, which are essential for developing sophisticated embedded systems.

One of the significant features of the 8XC251 family is its integrated peripherals, including timer/counters, serial communication interfaces, and interrupt systems. These peripherals enable developers to implement timing functions, data communication, and real-time processing, all of which are crucial in modern embedded applications. The 8XC251SB and 8XC251SQ models, for instance, come equipped with multiple I/O ports that allow for interfacing with other devices and systems, enhancing their functionality in various environments.

The memory architecture of the 8XC251 devices is noteworthy, featuring on-chip ROM, RAM, and EEPROM. The on-chip memory allows for fast access times, which is essential for executing programs efficiently. Moreover, the EEPROM serves as non-volatile memory, enabling the storage of configuration settings and important data that must be retained even when power is lost.

In terms of operating voltage, the 8XC251 devices are designed to operate in a wide range, typically between 4.0V and 6.0V. This flexibility makes them suitable for battery-powered applications, where energy efficiency is critical. The power management features, including reduced power modes, further enhance their suitability for portable devices.

Lastly, the 8XC251 series is supported by a wide range of development tools and resources, allowing engineers and developers to streamline the development process. This support, combined with the microcontrollers' robust features, makes the Intel 8XC251 family a reliable choice for various embedded applications, such as industrial automation, automotive systems, and consumer electronics.

Overall, the Intel 8XC251SB, 8XC251SQ, 8XC251SA, and 8XC251SP deliver high performance, versatility, and ease of use, making them a preferred choice for embedded system designers looking to develop efficient and effective solutions.
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