CS THEORY - LOGIC, DATA TRANSMISSION, ERROR CHECKING, PROGRAMMING LANGUAGES AND TRANSLATORS

logic gate

a device that acts as a building block for digital circuits by performing a logical operation on one or more binary inputs to produce a single binary output.

NOT gate

a logic gate that inverts the input signal, producing a binary output that is the opposite of the input.

AND gate

a logic gate that outputs a binary high (1) signal only when all of its inputs are binary high (1).

OR gate

a logic gate that outputs a binary high (1) signal if at least one of its inputs is binary high (1).

NAND gate

a logic gate that outputs a binary low (0) signal only when all of its inputs are binary high (1).

NOR gate

a logic gate that outputs a binary low (0) signal if at least one of its inputs is binary high (1).

XOR gate

a logic gate that outputs a binary high (1) signal only when the number of its binary high inputs is odd.

simplex transmission

one direction - sending data to or recieving data from a device

half duplex data transmission

sending data to and from devices, both devices but only one at a time

full duplex (duplex)

both directions at the same time

interface

point at which two computers systems communicate

serial interface

interface to allow serial communication between the microcontroller or microprocessor using a serial cable

serial communication

• one bit of data is sent at a time

• slower, but less expensive than parallel bc only 1 data channel is used

• reliable over long distance

• less likely to get skewed at the recieving end bc only 1 wire is used

• easier to collate data after transmission than parallel

synchronised serial communication

the timing for when each bit is sent may be synchronised to the oscillations of an on-board clock

• reciever counts how many bits were sent and reassembles the bits into bytes

• timing must be accurate as no control bits are used. timing signals are sent WITH the data

  • it is faster as only data bits are sent

asynchronous serial communication

data is packaged and sent across to another device as a packet. files are broken up into many packets and reassembled at the receiving end.

format of a packet

frame

frame formats

defined by the protocol being used

USB

universal serial bus

advantages of all USB

• incorrect connections are prevented

• industry standard - compatibility

• devices can be charged and powered at the same time by a USB cable

  • doesnt require wireless, so can be used in a network is done

USB-C

• symmetrically double pins

  • can be inserted either way

• more power than older USBs

• most modern protocols can run over USB-c

parallel communication

• several bits bieing sent at the time on a link with several channels in parallel with each other

• fastest as multiple bits are sent over mmultiple wires or data channels at the same time

• allows read/write at the same time

• best for short distances as data can go out of synchronisation

uses of parallel transmission

• inside integrated circuits - tiny microchip computers in embedded systems eg washing machines and microwaves

  • inside the CPU of a computer system

why is parallel not used more widely

• signal degradation - long distances

• timing issues - data may be wrongly alligned

• complex design - take up more space

port

connection point or interface between a computer and en external or internal hardware device

software port

a virtual point where network connections start and end

protocols

sets of rules and standards for how data is transmitted and received over a network

what do protocols determine

• how data packets are structured

• encoding methods

• error detection

• addressing

• session persistance

• security

IDE

integrated development environment - where software programs are written eg pycharm, IDLE

bootloader (arduino)

piece of software that allows you to upload code you write to the arduino

open source hardware

where anyone can see the design specification of a physical object

parity error checking

• odd/even parity is agreed on by the communicating devices

• odd parity means in total there will be an odd number of 1s

• in every byte, 7 bits are data and 1 bit is the parity bit

• the parity bit allows adjustment so the overall number of 1s adds to the agreed parity

  • if parity is incorrect, an error is detected

time to live variable

• packets are designed with an expiration date called a TTL (time-to-live) or hop limit bc of the risk that packets will continue to pass from router to router indefinitely

• each packet has a place where it stores a numerical value determining how much longer it should continue to move through the network

• every time a router receives a packet, it subtracts 1 from the TTL (common no for TTL is 64)

  • if TTL is 0, the router will discard the packet and send a message back to the originating host

high level languages

• can be used on many different types of computer

• programmer doesnt need knowledge of hardware - can focus on problem being solved

• uses english-like statements, easier for people to process

  • can use an IDE to code in high-level languages

low level languages

• machine code is the lowest level language

  • other low level languages such as assembly code work at the same level as machine code and may use mnemonics to represent each machine code instructions

low level languages benefits

• low level code can use machine-specific functions bc it directly works with registers and the CPU

• instructions can be executed faster

  • translated programmes use less memory

low level language disadvantages

• difficult to understand

• need to manipulate memory locations

• machine dependent

• error prone

programming languages

• arduino language is high level bc it uses words from English

• processor on the arduino executes the instructions which have been translated to 0s and 1s

machine code

instructions in the form of binary signals aka low level code

compiled vs interpreted languages

• C based languages are compiled

• python is interpreted

compilers

• compile the whole code at once and produce:

  • an executable code file

  • error report

• compiled programmes CAN be run without the compiler

• single high level language statement might end up stores as several machine code instructions

• benefits:

  • fast executionable code that runs directly on the processor

  • no need for translation software (platform independent)

  • source code cant be modified

• disadvantages

  • more difficult to debug

  • comments/source code arent visible once compiled

  • future changes - code needs to be recompiled

interpreters

• interpreter checks the code one line at a time and executes that line straight away and stops completely if an error is found

• interpreted programs CANT be run without the interprester

• a single high level language statement might mean executing several machine code in

• benefits:

  • interpreting makes it easier to debug code as errors are displayed as soon as they are found

• disadvantages:

  • speed of execution of program loops is slower as each line has to be interpreted individually every time its run

assemblers

• whole low level programme is translated from mnemonics into one executable machine code programmme

• a new, executable file is made

• assembled CAN be used without the assmebler

byte code

byte code needs to be interpreted or compiled at runtime time, but it achieves platform independence

platform independence

your code can be run on any machine