USB

1. It is a bus between host system and number of interconnected different devices.
2. 127 devices can connect to a host.
3. It provides fast as well as slow speed serial transmission and reception between host and serial devices.
4. A USB host, which includes controller for function as bus master can connect flash memory cards, digital camera.
5. A USB device can be hot plugged, configured and used, reset, reconfigured and used. It can share bandwidth with other devices, detached and re-attached. Attach and reattach could be done without rebooting.
6. UBI has four cables, one for +5V, 2 for twisted pairs and 1 for ground. USB is a polled bus.
7. The cable length is maximum up to 16 ft/segment. There can be maximum six cascaded segments in a network. The maximum post to device distance can be 96 feet.

USB Connector:

Type A – USB A (upstream) Type B – USB B (downstream)

USB Network

• USB network is a tree network with device ID field of 7 bits. Therefore, 2^7=128 IDs are available. ID0 is a sin to the host and therefore maximum 127 devices can be connected in the network.
• UBI network is host to device network where all devices can communicate with host and vice versa but a USB device cannot directly communicate with another USB device.

• Protocol - synchronous, half-duplex, serial data communication with differential data.

  

Logic levels

USB supports three types of pipes-

USB Speeds:

Signal Interface

Modbus

i) Modbus is a serial communication protocol developed by Modicon published by Modicon® in 1979 for use with its programmable logic controllers (PLCs).

ii) In simple terms, it is a method used for transmitting information over serial lines between electronic devices.

iii) The device requesting the information is called the Modbus Master and the devices supplying information are Modbus Slaves.

iv) In a standard Modbus network, there is one Master and up to 247 Slaves, each with a unique Slave Address from 1 to 247. The Master can also write information to the Slaves.

v) Working of Modbus –

• Modbus is transmitted over serial lines between devices.
• The simplest setup would be a single serial cable connecting the serial ports on two devices, a Master and a Slave.
• The data is sent as series of ones and zeroes called bits.
• Each bit is sent as a voltage. Zeroes are sent as positive voltages and ones as negative.

• The bits are sent very quickly. A typical transmission speed is 9600 baud (bits per second).

  

vi) Modbus is an open protocol, meaning that it's free for manufacturers to build into their equipment without having to pay royalties.

vii) It has become a standard communications protocol in industry, and is now the most commonly available means of connecting industrial electronic devices. It is used widely by many manufacturers throughout many industries.

viii) Modbus is typically used to transmit signals from instrumentation and control devices back to a main controller or data gathering system, for example a system that measures temperature and humidity and communicates the results to a computer.

ix) Modbus is often used to connect a supervisory computer with a remote terminal unit (RTU) in supervisory control and data acquisition (SCADA) systems.

x) Versions of the Modbus protocol exist for serial lines (Modbus RTU and Modbus ASCII) and for Ethernet (Modbus TCP).