data transmissions

simplex

data is only sent in one direction e.g. microphones

half duplex

data is sent to and from devices, data is sent in both directions but only one at a time e.g. instant messaging, walkie talkie

full duplex

data is sent in both directions at the same time e.g. telephone calls, broadband

interface

the point at which two devices communicate

serial interface

this is an interface to allow serial communication between the microcontroller and another microcontroller or microprocessor using a serial cable. There is one wire to transmit and one wire to receive.

serial communication

the process of sending data over one bit at a time sequentially over a single communication channel

synchronized serial communication

The timing for when each bit is sent may be synchronised to the oscillations of an on-board clock (CLK). Continuous stream of data + timing signals generated by internal clock to synchronise sending & receiving signals.

asynchronous serial communication

Alternatively, and more commonly, data may be packaged and sent across to another device as a packet. Files are broken up into many packets and reassembled at the receiving end. The format of the packet is its frame

how do frames work

Frame formats are defined by the protocol being used. Communicating devices agree a protocol, e.g. a bit pattern before transmission and a bit rate (bits per second). Typical bit rates are 9600bps. This is slightly slower than synchronous transmission, as more bits are sent. the frame format has all the information required to interpret the data at the receiving end

USB

Universal Serial Bus (USB) - external data transfer between devices When a USB device is plugged into a computer’s USB port: i) The device is automatically detected ii) Known devices are automatically recognized and their device driver is loaded by the OS iii) If not known, the OS searches its device driver. If not found, the user is prompted to download it. uses serial communication

advantages of usb

Incorrect connections are prevented as Old USB connectors only fit one way. Newer USB C connectors fit both ways and work both ways.

Industry standard: lots of compatibility & support available

Different data transmission rates are supported—some are very fast

Automatically detects if the correct driver is installed

Some devices (e.g. mobile phones) can be charged AND powered at the same time by using a USB cable

Some USB standards are backwards compatible

disadvantages of USB

Max cable length only 5 metres

Older standard (1.1) becoming obsolete