Embedded Systems Introduction

Embedded Systems

• A system is a set of components that follow a set of rules to achieve a specific task, and if one part fails, the system will stop working.
• An embedded system (ES) is a computer hardware system with software embedded in it, consisting of components like CPU, RAM, ROM, I/O Ports, and Timers on a single chip.
• ES can be an independent system or part of a large system, designed to perform a specific task, such as a fire alarm that senses only smoke.

Applications of Embedded Systems

• Medical equipment
• Home devices (digital alarm, air conditioner, washing machines)
• Automobiles (lighting system, door locks, air bags, anti-stealing alarms)
• Industrial control (robots, control system)
• Traffic lights
• Mobile phones

Components of Embedded Systems

• Sensor
• Microcontroller
• Memory
• Actuator (motor)
• Microcontroller is the most important part, controlling all operations required from it.

Embedded System Designer

• Must have knowledge of both microprocessors and microcontrollers.
• Note: An embedded system is a microcontroller-based system (special purpose), while a personal computer (PC) is a microprocessor-based system (general purpose).

Instruction Categories

• Arithmetic, logic, and shift instructions (INC, DEC, ADD, SUB, MUL, DIV, AND, OR, XOR, SHR, SHL)
• Instructions for moving information to and from memory and processor registers (MOV, LDA, STA, PUSH, POP)
• Control instructions (JMP, JZ, JNZ, SKI, SKO, CALL, RET)
• Input/output (I/O) instructions (INP, OUT)

Directives (Pseudo-ops)

• Define statement: allocates storage in data segment (DB, DW, DD)
• DUP (…) pseudo-op: multiplies the store of the same value in memory (data segment)
• ORG (origin) pseudo-op: tells MASM to reach the required offset address

Computer Instruction

• Is a binary code that specifies a sequence of micro-operations for the computer
• Is organized according to a certain instruction format

Instruction Format

• Op code field: specifies the operation (add, sub, mul, shift, complement, …)
• Address field: specifies the addresses of processor registers or memory words
• Mode field: specifies the way the operand or the effective address is determined

Addressing Modes

• Implied addressing mode: address of the operands are specified implicitly in the instruction
• Immediate addressing mode: operand itself is specified, no need to specify address
• Direct addressing mode: instruction specifies the memory address used directly to physical memory
• Indirect addressing mode: address field specifies the address of a memory location that contains the address of the operand