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Serial Port Communication In Asp.net C#

My asp.net application has to connect to a serial port to get weights occasionally. But since its not possible to do this directly from ASP.net, I am using a WCF service. How do I do this using WCF service? How do I get value back to the asp.net function? In serial port communication, the data is received in a separate thread. Jan 12, 2004 Web resources about - Serial Port Communication - asp.net.web-forms Communication - Wikipedia, the free encyclopedia) is the activity of conveying information through the exchange of ideas, feelings, intentions, attitudes, expectations, perceptions or commands. VoIP Business, VoIP Technology, VoIP Security - Fierce Enterprise Communications. In computing, a serial port is a serial communication interface through which information transfers in or out sequentially one bit at a time. This is in contrast to a parallel port, which communicates multiple bits simultaneously in parallel.Throughout most of the history of personal computers, data has been transferred through serial ports to devices such as modems, terminals, various. Oct 31, 2019 Unless the scale, communicating over a serial port, is directly connected to the web server you can't talk to the scale. As you've probably figured out by now, client-side javascript in a browser has no access to the PC's serial ports. Javascript can only talk to other web servers.

Considered to be one of the most basic external connections to a computer, the serial port has been an integral part of most computers for more than 20 years. Although many of the newer systems have done away with the serial port completely in favor of USB connections, most modems still use the serial port, as do some printers, PDAs and digital cameras. Few computers have more than two serial ports.

Essentially, serial ports provide a standard connector and protocol to let you attach devices, such as modems, to your computer. In this edition of How Stuff Works, you will learn about the difference between a parallel port and a serial port, what each pin does and what flow control is.

Contents

All computer operating systems in use today support serial ports, because serial ports have been around for decades. Parallel ports are a more recent invention and are much faster than serial ports. USB ports are only a few years old, and will likely replace both serial and parallel ports completely over the next several years.

The name 'serial' comes from the fact that a serial port 'serializes' data. That is, it takes a byte of data and transmits the 8 bits in the byte one at a time. The advantage is that a serial port needs only one wire to transmit the 8 bits (while a parallel port needs 8). The disadvantage is that it takes 8 times longer to transmit the data than it would if there were 8 wires. Serial ports lower cable costs and make cables smaller.

Before each byte of data, a serial port sends a start bit, which is a single bit with a value of 0. After each byte of data, it sends a stop bit to signal that the byte is complete. It may also send a parity bit.

Serial ports, also called communication (COM) ports, are bi-directional. Bi-directional communication allows each device to receive data as well as transmit it. Serial devices use different pins to receive and transmit data -- using the same pins would limit communication to half-duplex, meaning that information could only travel in one direction at a time. Using different pins allows for full-duplex communication, in which information can travel in both directions at once.

Serial ports rely on a special controller chip, the Universal Asynchronous Receiver/Transmitter (UART), to function properly. The UART chip takes the parallel output of the computer's system bus and transforms it into serial form for transmission through the serial port. In order to function faster, most UART chips have a built-in buffer of anywhere from 16 to 64 kilobytes. This buffer allows the chip to cache data coming in from the system bus while it is processing data going out to the serial port. While most standard serial ports have a maximum transfer rate of 115 Kbps (kilobits per second), high speed serial ports, such as Enhanced Serial Port (ESP) and Super Enhanced Serial Port (Super ESP), can reach data transfer rates of 460 Kbps.

The external connector for a serial port can be either 9 pins or 25 pins. Originally, the primary use of a serial port was to connect a modem to your computer. The pin assignments reflect that. Let's take a closer look at what happens at each pin when a modem is connected.

9-pin connector:

Carrier Detect - Determines if the modem is connected to a working phone line.
Receive Data - Computer receives information sent from the modem.
Transmit Data - Computer sends information to the modem.
Data Terminal Ready - Computer tells the modem that it is ready to talk.
Signal Ground - Pin is grounded.
Data Set Ready - Modem tells the computer that it is ready to talk.
Request To Send - Computer asks the modem if it can send information.
Clear To Send - Modem tells the computer that it can send information.
Ring Indicator - Once a call has been placed, computer acknowledges signal (sent from modem) that a ring is detected.

25-pin connector:

Not Used
Transmit Data - Computer sends information to the modem.
Receive Data - Computer receives information sent from the modem.
Request To Send - Computer asks the modem if it can send information.
Clear To Send - Modem tells the computer that it can send information.
Data Set Ready - Modem tells the computer that it is ready to talk.
Signal Ground - Pin is grounded.
Received Line Signal Detector - Determines if the modem is connected to a working phone line.
Not Used: Transmit Current Loop Return (+)
Not Used
Not Used: Transmit Current Loop Data (-)
Not Used
Not Used
Not Used
Not Used
Not Used
Not Used
Not Used: Receive Current Loop Data (+)
Not Used
Data Terminal Ready - Computer tells the modem that it is ready to talk.
Not Used
Ring Indicator - Once a call has been placed, computer acknowledges signal (sent from modem) that a ring is detected.
Not Used
Not Used
Not Used: Receive Current Loop Return (-)

Voltage sent over the pins can be in one of two states, On or Off. On (binary value '1') means that the pin is transmitting a signal between -3 and -25 volts, while Off (binary value '0') means that it is transmitting a signal between +3 and +25 volts..

An important aspect of serial communications is the concept of flow control. This is the ability of one device to tell another device to stop sending data for a while. The commands Request to Send (RTS), Clear To Send (CTS), Data Terminal Ready (DTR) and Data Set Ready (DSR) are used to enable flow control.

Let's look at an example of how flow control works: You have a modem that communicates at 56 Kbps. The serial connection between your computer and your modem transmits at 115 Kbps, which is over twice as fast. This means that the modem is getting more data coming from the computer than it can transmit over the phone line. Even if the modem has a 128K buffer to store data in, it will still quickly run out of buffer space and be unable to function properly with all that data streaming in.

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With flow control, the modem can stop the flow of data from the computer before it overruns the modem's buffer. The computer is constantly sending a signal on the Request to Send pin, and checking for a signal on the Clear to Send pin. If there is no Clear to Send response, the computer stops sending data, waiting for the Clear to Send before it resumes. This allows the modem to keep the flow of data running smoothly.

Introduction

In order to make two devices communicate, whether they are desktop computers, microcontrollers, or any other form of computer, you need a method of communication and an agreed-upon language. Serial communication is one of the most common forms of communication between computers. These notes explain the basics of getting two computers talking to each other using Asynchronous Serial communication.

To get the most out of these notes, you should know what a microcontroller is and have an understanding of the basics of microcontroller programming. You should have some understanding of programming a personal computer as well, ideally in a language that can access the serial ports of the computer, like the Processing programming environment, node.js programming environment, Python, or Java.

Serial Communication Agreements

Communicating serially involves sending a series of digital pulses back and forth between devices at a mutually agreed-upon rate. The sender sends pulses representing the data to be sent at the agreed-upon data rate, and the receiver listens for pulses at that same rate. This is what’s known as asynchronous serial communication. There isn’t a common clock in asynchronous serial communication; instead, both devices keep time independently, and either send or listen for new bits of data at an agreed-upon rate.

In order to communicate, the two devices need to agree on a few things:

the rate at which data is sent and read
the voltage levels representing a 1 or a 0 bit
the meaning of those voltage levels; is a high voltage 1 and a low voltage 0, or is the signal inverted so that a low voltage is a 1 and high voltage is 0?

For example, let’s say two devices are to exchange data at a rate of 9600 bits per second. First, you would make sure there’s an agreed upon high and low voltage supplying each device, then you’d make three connections between the two devices:

a common ground connection, so both devices have a common reference by which to measure voltage;
one wire for the sender to send data to the receiver on (transmit line for the sender);
one wire for the receiver to send date to the sender on (receive line for the sender).

Since the data rate is 9600 bits per second (sometimes called 9600 baud), the receiver will read the voltage on its receive wire every 1/9600th of a second. It will interpret that voltage reading as a new bit of data. If the voltage is high (typically +5V or +3.3V in the case of most microcontrollers), it will interpret that bit of data as a 1. If it is low (typically 0V), it will interpret that bit of data as a 0. By interpreting the bits of data over time, the receiver can get a detailed message from the sender. at 9600 baud, for example, 1200 bytes of data can be exchanged in one second.

What Do the Serial Voltage Changes Mean?

Let’s look at a byte of data being exchanged. Imagine you want to send the number 90 from one device to another. First, you have to convert the number from the decimal representation 90 to a binary representation. In binary, 90 is 01011010. So your sending device will pulse its transmit line as shown in Figure 1:

As you might guess from this diagram, both devices also have to agree on the order of the bits. Usually the sender sends the highest bit (or most significant bit) first in time, and the lowest (or least significant bit) last in time. As long as you have an agreed upon voltage, data rate, order of interpretation of bits, and agreement on what the voltage levels mean, you can exchange any data you want serially.

For the data transmission above, a high voltage indicates a bit value of 1, and a low voltage indicates a voltage of 0. This is known as true logic. Some serial protocols use inverted logic, meaning that a high voltage indicates a logic 0, and a low voltage indicates a logic 1. It’s important to know whether your protocol is true or inverted. For example, RS-232, which was the standard serial protocol for most personal computers before USB came along, uses inverted logic.

UART? USB? CDC?

The asynchronous serial communication you’ll be using here is sometimes referred to as TTL serial, and it’s not an inverted serial protocol. In TTL serial communications, high voltage means logic 1, and low voltage means logic 0. Most processors on the market today are equipped with one or more Universal Asynchronous Receiver-Transmitters, or UARTs, for communicating this way.

Most personal computers do not have an asynchronous serial port anymore. Instead, they have USB ports. USB stands for Universal Serial Bus, and it’s a slightly different serial protocol that allows multiple devices to communicate over the same wires. This configuration is known as a bus configuration. USB is a complex protocol that can support many different classes of devices, from human interface devices (HID) like mice and keyboards to mass storage devices to cameras, and more. Because so many devices still use asynchronous serial communication, USB includes a Communications Device Class (CDC) that supports asynchronous serial communication. Devices that include a USB-to-serial converter will show up as serial ports to your computer when you plug them in. Many microcontroller boards, including the Arduino boards, include a USB-to-serial converter to communicate with your computer in this way. When you plug them in, any program that can read serial ports will list the connected Arduino in the list of serial ports.

Serial Buffers and Control of the Port

Once you’ve got the computer and the microcontroller connected, you’ll need to write a program to address the serial ports. The process is slightly different on the different microcontrollers, but there are some elements common to all of them.

All processors that have a UART (this includes personal computers and microcontrollers, and most embedded boards like the Beaglebone Black and Raspberry Pi as well) have an area in memory where they store incoming data from the serial ports called a serial buffer. Because of this, they can do other tasks while waiting for data to come in, and act on the data from the buffer after it comes in.

Serial ports can only be controlled by one program at a time. For microcontrollers that aren’t running an operating system, this is simple; whatever program is running on the controller gets the serial port. On computers with an operating system, you might have multiple programs running, but only one can control a given serial port at any one time. For example, if you have a laptop connected serially to an Arduino, and the Arduino IDE’s Serial Monitor is open, then no other program can read from that serial port. You’d need to close the serial monitor to open the port from Processing or any other application. Related video: Only one program can control the port

Once you’ve got the serial port open, any bytes sent by the connected device will be available to your program in the order that they were sent. As you read each byte, the byte is removed from the serial buffer. This is why serial buffers are also called First-In, First-Out or FIFO buffers.

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See the Arduino serial lab, the Serial Input to the P5.js IDE lab or the Serial Communication with Node.js lab for more on sending serial from Arduino to another computer.

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Serial Port Communication In Asp.net C#

When two devices are communicating serially, they can’t read each other’s program logic. They can only read what the other device has said. Because of this, you need to make sure that the programs on both sides are using the same communications protocol. This is the highest level of agreement in serial communications: both sides need to agree on what the bytes being sent mean, and in what order they are being sent. For more on this, see the serial data interpretation notes.