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Parallel Port
Serial Port Protocol Specification
Arduino Serial Port Protocol

Implement a serial port read loop and dispatch to a Protocol instance (like the asyncio.Protocol) but do it with threads. Calls to close will close the serial port but it is also possible to just stop this thread and continue to use the serial port instance otherwise. init (serialinstance, protocolfactory) ¶. Serial Port Redirector is a software that provides access to remote serial devices over TCP/IP network. The program creates virtual COM ports and redirects all data and signals written to the port to the remote host with specified IP-address and TCP-port. Arduino built-in functions for sending/receiving data are not very handy and sturdy. We introduce a protocol to communicate (using serial port, bluetooth or sockets) with the Arduino (but not only.

This topic describes how to use My.Computer.Ports to receive strings from the computer's serial ports in Visual Basic.

To receive strings from the serial port

Initialize the return string.
Determine which serial port should provide the strings. This example assumes it is COM1.
Use the My.Computer.Ports.OpenSerialPort method to obtain a reference to the port. For more information, see OpenSerialPort.
The Try...Catch...Finally block allows the application to close the serial port even if it generates an exception. All code that manipulates the serial port should appear within this block.
Create a Do loop for reading lines of text until no more lines are available.
Use the ReadLine() method to read the next available line of text from the serial port.
Use an If statement to determine if the ReadLine() method returns Nothing (which means no more text is available). If it does return Nothing, exit the Do loop.
Add an Else block to the If statement to handle the case if the string is actually read. The block appends the string from the serial port to the return string.
Return the string.

Example

This code example is also available as an IntelliSense code snippet. In the code snippet picker, it is located in Connectivity and Networking. For more information, see Code Snippets.

Compiling the Code

This example assumes the computer is using COM1.

Robust Programming

This example assumes the computer is using COM1. For more flexibility, the code should allow the user to select the desired serial port from a list of available ports. For more information, see How to: Show Available Serial Ports.

This example uses a Try...Catch...Finally block to make sure that the application closes the port and to catch any timeout exceptions. For more information, see Try...Catch...Finally Statement.

There are many different reasons to use a serial interface. One of the most common is the need to interface with a PC, during development and/or in the field. Most, if not all PCs have some sort of serial bus interface available to connect peripherals. For embedded systems that must interface with a general-purpose computer, a serial interface is often easier to use than the ISA or PCI expansion bus.

A benefit of serial communications is low pin counts. Serial communications can be performed with just one I/O pin, compared to eight or more for parallel communications. Many common embedded system peripherals, such as analog-to-digital and digital-to-analog converters, LCDs, and temperature sensors, support serial interfaces.

Serial buses can also provide for inter-processor communication-a network, if you will. This allows large tasks that would normally require larger processors to be tackled with several inexpensive smaller processors. Serial interfaces allow processors to communicate without the need for shared memory and semaphores, and the problems they can create.

This isn't to say that parallel buses have no use. For operational fetches, address and data buses, and other microprogram control, parallel buses have always been the clear winner. 'Memory-mapping' peripherals has been a technique commonly used for systems with address and data buses. This tendency allows parallel access to off-chip peripherals. However, with many 8-bit microcontrollers (let alone 8-pin) with no external address/data bus available for designs, memory-mapping is not an option.

Terminology

Before we get into the individual interface details, we should define several terms:

On an asynchronous bus, data is sent without a timing clock. A synchronous bus sends data with a timing clock.
Full-duplex means data can be sent and received simultaneously. Half-duplex is when data can be sent or received, but not at the same time.
Master/slave describes a bus where one device is the master and others are slaves. Master/slave buses are usually synchronous, as the master often supplies the timing clock for data being sent along in both directions.
A multi-master bus is a master/slave bus that may have more than one master. These buses must have an arbitration scheme that can settle conflicts when more than one master wants to control the bus at the same time.
Point-to-point or peer interfaces are where two devices have a peer relation to each other; there are no masters or slaves. Peer interfaces are most often asynchronous.
The term multi-drop describes an interface in which there are several receivers and one transmitter.
Multi-point describes a bus in which there are more than two peer transceivers. This is different from a multi-drop interface as it allows bidirectional communication over the same set of wires.

RS-232

TIA/EIA-232-F (typically referred to as RS-232) is a common interface that can be found on almost every personal computer. RS-232 is a complete standard, not only including electrical characteristics, but physical and mechanical characteristics as well, such as connection hardware, pin-outs, and signal names. A point-to-point interface, RS-232 is capable of moderate distances at speeds up to 20Kbps. While not specifically called out in the specification, speeds of greater than 115.2Kbps are possible, provided that connections are short and proper grounding is used. Cable lengths of 30 feet are common, and cables of over 200 feet can be attained with low-capacitance cable.

An RS-232 bus is an unbalanced bus capable of full-duplex communication between two receiver/transmitter pairs, named data terminal equipment (DTE) and data communication equipment (DCE). Each one has a transmit signal that is connected to the receive signal on the other end. As such, there is a pin difference between the two sides. (Your PC

To receive strings from the serial port

Example

Compiling the Code

Robust Programming

See also

Serial Port Protocol