What is Embedded System?
Embedded system employs a combination of software & hardware to perform a specific function. It is a part of a larger system which may not be a “computer”Works in a reactive & time constrained environment.
In embedded systems, the software is permanently set into a read-only memory such as a ROM or flash memory chip, in contrast to a general-purpose computer that loads its programs into RAM each time.
There are two types of Microcontroller architecture designed for embedded system development. These are:
1)RISC- Reduced instruction set computer
2)CISC- Complex instruction set computer
DIFFERENCE BETWEEN CISC AND RISC:
CISC stands for Complex Instruction Set Computer. Most PC's use CPU based on this architecture. For instance Intel and AMD CPU's are based on CISC architectures. Typically CISC chips have a large amount of different and complex instructions. In common CISC chips are relatively slow (compared to RISC chips) per instruction, but use little (less than RISC) instructions. MCS-51 family microcontrollers based on CISC architecture.
RISC stands for Reduced Instruction Set Computer. The philosophy behind it is that almost no one uses complex assembly language instructions as used by CISC, and people mostly use compilers which never use complex instructions. Therefore fewer, simpler and faster instructions would be better, than the large, complex and slower CISC instructions. However, more instructions are needed to accomplish a task. Atmell’s AVR microcontroller based on RISC architecture.
PIC MICROCONTROLLERS
PIC is a family of Harvard architecture microcontrollers made by Microchip Technology, derived from the PIC1640 originally developed by General Instrument's Microelectronics Division. The name PIC initially referred to "Peripheral Interface Controller".It is available in different configurations such as 8bit,16 bit,32 bit with instructions set as given below :
Under 8 bit comes- PIC10 xxxx, PIC12 xxxx, PIC16 xxxx, PIC18 xxxx.
(12 bit instruction set)
Under 16 bit comes- PIC24H,DSPIC30,DSPIC33. (14 bit instruction set)
Under 32 bit comes- PIC32xxxx. (16 bit instruction set)
The main features of PIC architecture is as follows
>> Separate code and data spaces (Harvard architecture)
>>A small number of fixed length instructions
>> Most instructions are single cycle execution (4 clock cycles), with single delay cycles upon branches and skips
>>A single accumulator (W), the use of which (as source operand) is implied (i.e. is not encoded in the op code)
>>All RAM locations function as registers as both source and/or destination of math and other functions.
>>A hardware stack for storing return addresses
>>A fairly small amount of addressable data space (typically 256 bytes), extended through banking
>>Data space mapped CPU, port, and peripheral registers
>>The program counter is also mapped into the data space and writable (this is used to implement indirect jumps).
>>Unlike most other CPUs, there is no distinction between memory space and register space because the RAM serves the job of both memory and registers, and the RAM is usually just referred to as the register file or simply as the registers
PIC is a family of Harvard architecture microcontrollers made by Microchip Technology, derived from the PIC1640 originally developed by General Instrument's Microelectronics Division. The name PIC initially referred to "Peripheral Interface Controller".It is available in different configurations such as 8bit,16 bit,32 bit with instructions set as given below :
Under 8 bit comes- PIC10 xxxx, PIC12 xxxx, PIC16 xxxx, PIC18 xxxx.
(12 bit instruction set)
Under 16 bit comes- PIC24H,DSPIC30,DSPIC33. (14 bit instruction set)
Under 32 bit comes- PIC32xxxx. (16 bit instruction set)
>> Separate code and data spaces (Harvard architecture)
>>A small number of fixed length instructions
>> Most instructions are single cycle execution (4 clock cycles), with single delay cycles upon branches and skips
>>A single accumulator (W), the use of which (as source operand) is implied (i.e. is not encoded in the op code)
>>All RAM locations function as registers as both source and/or destination of math and other functions.
>>A hardware stack for storing return addresses
>>A fairly small amount of addressable data space (typically 256 bytes), extended through banking
>>Data space mapped CPU, port, and peripheral registers
>>The program counter is also mapped into the data space and writable (this is used to implement indirect jumps).
>>Unlike most other CPUs, there is no distinction between memory space and register space because the RAM serves the job of both memory and registers, and the RAM is usually just referred to as the register file or simply as the registers
