3. Interface to physical world
Embedded systems interface with the physical world through Sensors and Actuators. Sensors act as “senses” for an embedded system, whereas actuators act as “limbs”. Varieties of sensors working on variety of sensing principles are used in embedded systems. Light, temperature, acceleration, speed, mass, distance, etc. are common physical parameters which are sensed. Motors are one of the actuators used in many systems.
These transducers interface to the processor through variety of interfaces:
. Serial Communication Interfaces (SCI): RS-232, RS-422, RS-485 etc
. Synchronous Serial Communication Interface: I2C, SPI
. Universal Serial Bus (USB)
. Networks: Ethernet, Controller Area Network(CAN), etc
. Discrete IO: General Purpose Input/ Output (GPIO)
. Analog to Digital/Digital to Analog Converter (ADC/DAC).
RELEVANT IMPORTANT CONCEPTS
1. Computer Architecture
Two common prevalent processor architectures are Neumann Vs Harvard. Von Neumann architectures have same program and data memory space; both shares address bus and data bus. Harvard architecture has different memory space for program and data. For each of them, separate data bus and address bus are provided.
2. Instruction Set Architecture(ISA)
RISC has simple primitiveinstructions and addressing modes. The instructions are of uniform length, execute in one clock cycle & support pipelining. CISC chips have a large amount of variable length, different and complex instructions and take longer than a clock cycle to execute.
CISCchips are relatively slow per instruction compared to RISC chips, but usefewer instructions than RISC. Thus, RISC systems shorten execution time by reducing the clock cycles per instruction, whereas CISC shorten execution time by reducing MIPS R2000 is a typical product of pure RISC and Intel 80386 is a typical kind of pure CISC chip.