8XC251SA, SB, SP, SQ USER’S MANUAL

A.4 INSTRUCTION DESCRIPTIONS

This section describes each instruction in the MCS 251 architecture. See the note on page A-11 regarding execution times.

Table A-28 defines the symbols (—, ✓, 1, 0,?) used to indicate the effect of the instruction on the flags in the PSW and PSW1 registers. For a conditional jump instruction, “!” indicates that a flag influences the decision to jump.

Table A-28. Flag Symbols

Symbol

Description

—The instruction does not modify the flag.

✓The instruction sets or clears the flag, as appropriate.

1 The instruction sets the flag.

0 The instruction clears the flag.

? The instruction leaves the flag in an indeterminate state.

!For a conditional jump instruction: The state of the flag before the instruction executes influences the decision to jump or not jump.

ACALL <addr11>

Function:

Absolute call

Description: Unconditionally calls a subroutine at the specified address. The instruction increments the 3- byte PC twice to obtain the address of the following instruction, then pushes bytes 0 and 1 of the result onto the stack (byte 0 first) and increments the stack pointer twice. The destination address is obtained by successively concatenating bits 15–11 of the incremented PC, opcode bits 7–5, and the second byte of the instruction. The subroutine called must therefore start within the same 2-Kbyte “page” of the program memory as the first byte of the instruction following ACALL.

Flags:

CY

 

AC

 

OV

 

N

Z

 

 

 

 

 

 

 

 

 

 

 

 

—

 

—

 

—

 

—

—

Example:

 

 

 

 

 

 

The stack pointer (SP) contains 07H and the label "SUBRTN" is at program memory location

 

0345H. After executing the instruction

 

 

 

 

 

ACALL SUBRTN

 

 

 

 

 

 

 

 

 

at location 0123H, SP contains 09H; on-chip RAM locations 08H and 09H contain 25H

 

and 01H, respectively; and the PC contains 0345H.

 

 

 

 

 

Binary Mode

Source Mode

 

 

 

 

Bytes:

2

 

 

2

 

 

 

 

 

 

States:

9

 

 

9

 

 

 

 

 

 

A-26

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Intel 8XC251SB, 8XC251SA, 8XC251SP, 8XC251SQ, Embedded Microcontroller Instruction Descriptions, Table A-28. Flag Symbols
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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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