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• Jamstix Serial Port Charlotte
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Despite the emergence of the new-generation ports like USB, the COM interface is still one of the most common communication channels for connecting computers with the outside world. But just like any other communication interface, RS232 ports can break down as a result of some negative impacts or misuse. Unfortunately, it’s not always obvious if the problem is with the COM interface or with the external device attached to it.

Luckily, there is a dedicated RS232 Test Software that allows testing and analyzing the activity of any serial port available in your system. A handy COM port test program can help you check the operability of any COM port and prevent any possible problems.

In this article, I’ll tell you about this advanced solution and describe how to test serial port communications in the simplest and most efficient way.

Contents

1. RS232 test software.
2. Advantages of using an RS232 Protocol Analyzer

RS232 testing software

Serial Port Monitor is a professional utility that gives developers a centralized place to record and display the data going through all tested serial ports. The app is designed to log everything a COM port does during a monitoring session, so programmers don’t have to document all actions by hand.

The solution differentiates from competitors in that it offers both a user-friendly GUI and a bunch of really outstanding features like built-in terminal, advanced filtering and search options, four convenient viewing modes, support for all types of serial interfaces, including RS232, RS422, RS485, and more.

Also, with this app, you will have the option of forwarding all monitored data to the specified file or copy the captured data to the clipboard.

Why choose RS232 tester software?

✔ Versatility. The software can be applied in a great variety of usage scenarios. It’s able to monitor, read, record, save, and analyze serial data going through a specified COM port or several ones at a time. Plus, the app will allow you to emulate sending data to the required port in different formats (string, binary, octal, decimal, hexadecimal, or mixed).

✔ Reliability. Serial Port Monitor is a stable utility that works equally well with all versions of Windows OS, including Windows 10 (both x32 and x64). What’s great is that all internal drivers of the app are digitally signed.

✔ The ease of use. The developers of the program have provided the app with an intuitive GUI which makes the process of COM port testing as simple and efficient as possible.

Why test RS232 ports?

As you may know, a wide range of specialized equipment such as lab instruments, industrial controllers, A/V devices employed in signal management systems, etc. communicate their data via serial interfaces. To be able to troubleshoot the problems appearing in serial device networks, maintenance specialists need to have specialized tools that will help them identify and resolve the issues they may face. The challenges are many and you can find the description of the most common ones in our RS232 troubleshooting guide.

So, if you have a decent serial port testing tool capable of displaying everything what’s happening in your serial network in real time, you can easily find the source of any problem and solve it with minimum efforts and time.

Scenario 1. Analyze COM port activity.

As an example of COM port testing software, I’ll use Serial Port Monitor by Eltima. Here’s what you should do if you need to analyze the activity of your system’s serial interfaces.

1. Download the app, install it on your computer and start it. After that, start a monitoring session in the following way:

2. Head to the main menu, select Session > New session. Alternatively, you can click ‘New’ on the main toolbar or use ‘Ctrl + N’ shortcut.

3. Once done, you’ll see the ‘New monitoring session’ screen.

There you should select the visualizer that will display captured serial data to you. There are four main viewing modes:

Table: shows the table consisting of the recorded IRPs;

Line: IRPs with details are displayed as a plain text in lines;

Dump: shows the outgoing and incoming serial data in hexadecimal and string formats;

Terminal: the data is displayed as ASCII characters.

As an option, you can enable ‘Select all’ or ‘Select none’.

4. Then, if you need to immediately begin your work, choose ‘Start monitoring now’. Also, you can start the monitoring session in new window by enabling the corresponding option.

5. Next, you go to the ‘Capture options’ that regulate which events will be captured – create/close, read/write, or device control.

6. Finally, click ‘Start monitoring’ and your session will be activated.

In case you need to save the session, choose ‘Session -> Save session/ Save session As’ on the main menu.

Scenario 2. Compare monitoring sessions.

After you have saved the monitoring session using your serial port test software, Serial Port Monitor, you can compare it with another session to see the differences.

To achieve this, just do the following:

1. Start or open a monitoring session;

2. On the main menu, choose Session>Compare Sessions;

3. Then, select the monitoring file you’d like to open;

4. Now, the two sessions will be displayed side-by-side so that you can easily compare and analyze them.

Scenario 3. Resend the same data to a serial port.

In order to test whether the problem in your serial network is fixed, you can reproduce the communication between a COM port and a serial app or device. Serial Port Monitor will help you resend the exact same data to the required COM port so that you can review the reaction of your serial software or device.

All you need to do is:

1. Start or open a monitoring session;

2. Choose Session>Reproduce and configure the necessary parameters:

Use port - specify a serial port that will be used in the reproduced communication.

Send requests to this port - enable this option if you want to send data to a serial port on behalf of a serial app.

Respond as a device - enable this option if you want to send data to a serial port on behalf of a serial device.

Preserve time intervals - use this option if you’d like your data packets to be sent with the time intervals.

Custom IO timeout - choose this option to specify Read/Write timeout parameters.

3. Click ‘Start’.

What is RS232 loopback test?

A loopback test is a diagnostic test in which the signal returns to the transmitter after passing through the communication channel in both directions. Simply put, you can use loopback test to determine whether the device is working right. This test allows sending and receiving data from the same serial port. This method will let you easily pin down a malfunctioning port and node in a serial device network.

How to perform a loopback test

A loopback test is a common way to troubleshoot RS232, RS422, and RS485 communications. It releases you of the need to connect to additional hardware in order to identify issues with a serial port, cable, or application generating requests. With the help of a loopback test, you can simulate a complete communications circuit. All that is required to do is temporarily connect the proper pins to allow signals to be sent and received on the same COM interface.

For RS-232 loopback test, you need to connect the transmit (TXD) pin to the receive (RXD) pin. In the differential RS-422 and RS-485 communications, you should connect the TXD+ pin to the RXD+ and the TXD- to the RXD-.

If you need to perform a more advanced loopback test which will allow hardware flow control, you should connect the CTS and RTS pins to the DTR and DSR pins in RS-232 port, and CTS+ with to RTS+; CTS- with RTS- in RS-422 and RS-485 ports.

Below you can see the pinout of a common serial connector, DE-9:

For a loopback test with no hardware flow control (marked red in Fig. 2,3 below), you connect:

• pins 2 and 3 for RS-232;
• pins 4 to 8 and 5 to 9 for RS-422/485.

For a loopback test with a hardware flow control (marked blue in Fig. 2,3), you connect:

• pins 4 to 6 (DTR/DSR hardware flow control) and 7 to 8 (RTS/CTS hardware flow control) for RS-232;
• pins 2 to 3 and 6 to 7 for RS-422/485. Note that since RS-422/485 have differential connections, both of these connections are needed.

The pin numbers are often engraved in the plastic of the connector. Here is how pins are called in DE9 connector of the RS-232 serial port:

Loopback Test in HyperTerminal

HyperTerminal is a program that allows your PC to function as a computer terminal and connect with other systems remotely. This program lets you interact with remote devices via a standard serial bus (RS-232) or using the telnet protocol.

As long as HyperTerminal supports data transfer via COM ports, you can use this program to perform a loopback test.

Here’s how it works:

1. In the HyperTerminal you establish a new connection and give it a name. Select the icon for your connection.


2. Specify the communications port that will be tested.


3. Choose the type of flow control you’ll use. Here you have several options: Xon/Xoff, hardware, and none. Keep in mind that Xon/Xoff is a software flow control, so if choosing this option, you only need the TXD and RXD pins to be connected.


4. Now, use your keyboard to type a message. Any data that shows in Hyperterminal is received from the device.

HyperTerminal is a convenient way to test you RS232 ports, but not the most efficient one.

The limited capabilities of this serial loopback test app won’t lead you to much success in controlling and debugging of your serial communications. More than that, if you’re going to use HyperTerminal on Windows 7 or 10, you should remember that these OS versions support only the private edition of the app, which is not free for commercial use.

Conclusion

There are many methods and solutions that can help you test and troubleshoot serial ports. In this article, I’ve highlighted the most common and popular ones. As you can see, Serial Port Monitor by Eltima stands out for its powerful and versatile functionality. This serial port test tool can be used not only as a great alternative to HyperTerminal but also as a great solution for development and debugging of serial apps and hardware.

Serial Port Monitor

In computing, a serial port is a serial communication interface through which information transfers in or out one bit at a time (in contrast to a parallel port).^[1] Throughout most of the history of personal computers, data was transferred through serial ports to devices such as modems, terminals, and various peripherals.

While such interfaces as Ethernet, FireWire, and USB all send data as a serial stream, the term serial port usually identifies hardware compliant to the RS-232 standard or similar and intended to interface with a modem or with a similar communication device.

Modern computers without serial ports may require USB-to-serial converters to allow compatibility with RS-232 serial devices. Serial ports are still used in applications such as industrial automation systems, scientific instruments, point of sale systems and some industrial and consumer products. Server computers may use a serial port as a control console for diagnostics. Network equipment (such as routers and switches) often use serial console for configuration. Serial ports are still used in these areas as they are simple, cheap and their console functions are highly standardized and widespread. A serial port requires very little supporting software from the host system.

• 1Hardware
• 3Settings

Hardware[edit]

Some computers, such as the IBM PC, use an integrated circuit called a UART. This IC converts characters to and from asynchronous serial form, implementing the timing and framing of data in hardware. Very low-cost systems, such as some early home computers, would instead use the CPU to send the data through an output pin, using the bit banging technique. Before large-scale integration (LSI) UART integrated circuits were common, a minicomputer would have a serial port made of multiple small-scale integrated circuits to implement shift registers, logic gates, counters, and all the other logic for a serial port.

Early home computers often had proprietary serial ports with pinouts and voltage levels incompatible with RS-232. Inter-operation with RS-232 devices may be impossible as the serial port cannot withstand the voltage levels produced and may have other differences that 'lock in' the user to products of a particular manufacturer.

Low-cost processors now allow higher-speed, but more complex, serial communication standards such as USB and FireWire to replace RS-232. These make it possible to connect devices that would not have operated feasibly over slower serial connections, such as mass storage, sound, and video devices.

Many personal computer motherboards still have at least one serial port, even if accessible only through a pin header. Small-form-factor systems and laptops may omit RS-232 connector ports to conserve space, but the electronics are still there. RS-232 has been standard for so long that the circuits needed to control a serial port became very cheap and often exist on a single chip, sometimes also with circuitry for a parallel port.

DTE and DCE[edit]

The individual signals on a serial port are unidirectional and when connecting two devices the outputs of one device must be connected to the inputs of the other. Devices are divided into two categories data terminal equipment (DTE) and data circuit-terminating equipment (DCE). A line that is an output on a DTE device is an input on a DCE device and vice versa so a DCE device can be connected to a DTE device with a straight wired cable. Conventionally, computers and terminals are DTE while modems and peripherals are DCE.

If it is necessary to connect two DTE devices (or two DCE devices but that is more unusual) a cross-over null modem, in the form of either an adapter or a cable, must be used.

Male and female[edit]

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Generally, serial port connectors are gendered, only allowing connectors to mate with a connector of the opposite gender. With D-subminiature connectors, the male connectors have protruding pins, and female connectors have corresponding round sockets.^[2] Either type of connector can be mounted on equipment or a panel; or terminate a cable.

Connectors mounted on DTE are likely to be male, and those mounted on DCE are likely to be female (with the cable connectors being the opposite). However, this is far from universal; for instance, most serial printers have a female DB25 connector, but they are DTEs.^[3]

Connectors[edit]

While the RS-232 standard originally specified a 25-pin D-type connector, many designers of personal computers chose to implement only a subset of the full standard: they traded off compatibility with the standard against the use of less costly and more compact connectors (in particular the DE-9 version used by the original IBM PC-AT). The desire to supply serial interface cards with two ports required that IBM reduce the size of the connector to fit onto a single card back panel. A DE-9 connector also fits onto a card with a second DB-25 connector. Starting around the time of the introduction of the IBM PC-AT, serial ports were commonly built with a 9-pin connector to save cost and space. However, presence of a 9-pin D-subminiature connector is not sufficient to indicate the connection is in fact a serial port, since this connector is also used for video, joysticks, and other purposes.

Some miniaturized electronics, particularly graphing calculators and hand-held amateur and two-way radio equipment, have serial ports using a phone connector, usually the smaller 2.5 or 3.5 mm connectors and use the most basic 3-wire interface.

Many models of Macintosh favor the related RS-422 standard, mostly using German mini-DIN connectors, except in the earliest models. The Macintosh included a standard set of two ports for connection to a printer and a modem, but some PowerBook laptops had only one combined port to save space.

Since most devices do not use all of the 20 signals that are defined by the standard, smaller connectors are often used. For example, the 9-pin DE-9 connector is used by most IBM-compatible PCs since the IBM PC AT, and has been standardized as TIA-574. More recently, modular connectors have been used. Most common are 8P8C connectors, for which the EIA/TIA-561 standard defines a pinout, while the 'Yost Serial Device Wiring Standard'^[4] invented by Dave Yost (and popularized by the Unix System Administration Handbook) is common on Unix computers and newer devices from Cisco Systems. 10P10C connectors can be found on some devices as well. Digital Equipment Corporation defined their own DECconnect connection system which is based on the Modified Modular Jack (MMJ) connector. This is a 6-pin modular jack where the key is offset from the center position. As with the Yost standard, DECconnect uses a symmetrical pin layout which enables the direct connection between two DTEs. Another common connector is the DH10 header connector common on motherboards and add-in cards which is usually converted via a cable to the more standard 9-pin DE-9 connector (and frequently mounted on a free slot plate or other part of the housing).

Pinouts[edit]

The following table lists commonly used RS-232 signals and pin assignments.^[5]

The signal ground is a common return for the other connections; it appears on two pins in the Yost standard but is the same signal. The DB-25 connector includes a second 'protective ground' on pin 1, which is intended to be connected by each device to its own frame ground or similar. Connecting this to pin 7 (signal reference ground) is a common practice but not recommended.

Note that EIA/TIA 561 combines DSR and RI,^[10][11] and the Yost standard combines DSR and DCD.

Powered serial port[edit]

Some serial ports on motherboards or add-in cards provide jumpers that select whether pin 1 of the DE-9 connector connects to DCD or a power supply voltage, and whether pin 9 of the DE-9 connector connects to RI or a power supply voltage. The power supply voltage can be +5V, +12V, +9V, or ground. (Selection varies by vendor.) The power is intended for use by point-of-sale equipment. Makers include Dell^[12], HP, and others^[13] (This is not an official standard.)

Hardware abstraction[edit]

Operating systems usually create symbolic names for the serial ports of a computer, rather than requiring programs to refer to them by hardware address.

Unix-like operating systems usually label the serial port devices /dev/tty*. TTY is a common trademark-free abbreviation for teletype, a device commonly attached to early computers' serial ports, and * represents a string identifying the specific port; the syntax of that string depends on the operating system and the device. On Linux, 8250/16550 UART hardware serial ports are named /dev/ttyS*, USB adapters appear as /dev/ttyUSB* and various types of virtual serial ports do not necessarily have names starting with tty.

The DOS and Windows environments refer to serial ports as COM ports: COM1, COM2,..etc. Ports numbered greater than COM9 should be referred to using the .COM10 syntax.^[14]

Common applications for serial ports[edit]

The RS-232 standard is used by many specialized and custom-built devices. This list includes some of the more common devices that are connected to the serial port on a PC. Some of these such as modems and serial mice are falling into disuse while others are readily available.

Serial ports are very common on most types of microcontroller, where they can be used to communicate with a PC or other serial devices.

• Dial-up modems
• Configuration and management of networking equipment such as routers, switches, firewalls, load balancers
• GPS receivers (typically NMEA 0183 at 4,800 bit/s)
• Bar code scanners and other point of sale devices
• LED and LCD text displays
• Satellite phones, low-speed satellite modems and other satellite based transceiver devices
• Flat-screen (LCD and Plasma) monitors to control screen functions by external computer, other AV components or remotes
• Test and measuring equipment such as digital multimeters and weighing systems
• Updating firmware on various consumer devices.
• Hobbyist programming and debugging MCU's
• Stenography or Stenotype machines
• Software debuggers that run on a second computer
• Industrial field buses
• Computer terminal, teletype
• Older digital cameras
• Networking (Macintosh AppleTalk using RS-422 at 230.4 kbit/s)
• Older GSMmobile phones
• IDEhard drive^[15][16]repair^[17][18]

Since the control signals for a serial port can be easily turned on and off by a switch, some applications used the control lines of a serial port to monitor external devices, without exchanging serial data. A common commercial application of this principle was for some models of uninterruptible power supply which used the control lines to signal loss of power, low battery, and other status information. At least some Morse code training software used a code key connected to the serial port, to simulate actual code use. The status bits of the serial port could be sampled very rapidly and at predictable times, making it possible for the software to decipher Morse code.

Settings[edit]

Many settings are required for serial connections used for asynchronous start-stop communication, to select speed, number of data bits per character, parity, and number of stop bits per character. In modern serial ports using a UART integrated circuit, all settings are usually software-controlled; hardware from the 1980s and earlier may require setting switches or jumpers on a circuit board. One of the simplifications made in such serial bus standards as Ethernet, FireWire, and USB is that many of those parameters have fixed values so that users cannot and need not change the configuration; the speed is either fixed or automatically negotiated. Often if the settings are entered incorrectly the connection will not be dropped; however, any data sent will be received on the other end as nonsense.

Speed[edit]

Serial ports use two-level (binary) signaling, so the data rate in bits per second is equal to the symbol rate in baud. A standard series of rates is based on multiples of the rates for electromechanical teleprinters; some serial ports allow many arbitrary rates to be selected. The port speed and device speed must match. The capability to set a bit rate does not imply that a working connection will result. Not all bit rates are possible with all serial ports. Some special-purpose protocols such as MIDI for musical instrument control, use serial data rates other than the teleprinter series. Some serial port systems can automatically detect the bit rate.

The speed includes bits for framing (stop bits, parity, etc.) and so the effective data rate is lower than the bit transmission rate. For example, with 8-N-1 character framing only 80% of the bits are available for data (for every eight bits of data, two more framing bits are sent).

Bit rates commonly supported include 75, 110, 300, 1200, 2400, 4800, 9600, 19200, 38400, 57600 and 115200 bit/s.^[20]Crystal oscillators with a frequency of 1.843200 MHz are sold specifically for this purpose. This is 16 times the fastest bit rate and the serial port circuit can easily divide this down to lower frequencies as required.

Data bits[edit]

The number of data bits in each character can be 5 (for Baudot code), 6 (rarely used), 7 (for true ASCII), 8 (for most kinds of data, as this size matches the size of a byte), or 9 (rarely used). 8 data bits are almost universally used in newer applications. 5 or 7 bits generally only make sense with older equipment such as teleprinters.

Most serial communications designs send the data bits within each byte LSB (least significant bit) first. This standard is also referred to as 'little endian.' Also possible, but rarely used, is 'big endian' or MSB (most significant bit) first serial communications; this was used, for example, by the IBM 2741 printing terminal. (See Bit numbering for more about bit ordering.) The order of bits is not usually configurable within the serial port interface. To communicate with systems that require a different bit ordering than the local default, local software can re-order the bits within each byte just before sending and just after receiving.

Parity[edit]

Parity is a method of detecting errors in transmission. When parity is used with a serial port, an extra data bit is sent with each data character, arranged so that the number of 1 bits in each character, including the parity bit, is always odd or always even. If a byte is received with the wrong number of 1s, then it must have been corrupted. However, an even number of errors can pass the parity check.

Electromechanical teleprinters were arranged to print a special character when received data contained a parity error, to allow detection of messages damaged by line noise. A single parity bit does not allow implementation of error correction on each character, and communication protocols working over serial data links will have higher-level mechanisms to ensure data validity and request retransmission of data that has been incorrectly received.

The parity bit in each character can be set to one of the following:

• None (N) means that no parity bit is sent at all.
• Odd (O) means that parity bit is set so that the number of 'logical ones' must be odd.
• Even (E) means that parity bit is set so that the number of 'logical ones' must be even.
• Mark (M) parity means that the parity bit is always set to the mark signal condition (logical 1).
• Space (S) parity always sends the parity bit in the space signal condition (logical 0).

Aside from uncommon applications that use the last bit (usually the 9th) for some form of addressing or special signaling, mark or space parity is uncommon, as it adds no error detection information. Odd parity is more useful than even, since it ensures that at least one state transition occurs in each character, which makes it more reliable. The most common parity setting, however, is 'none', with error detection handled by a communication protocol.

Stop bits[edit]

Stop bits sent at the end of every character allow the receiving signal hardware to detect the end of a character and to resynchronise with the character stream. Electronic devices usually use one stop bit. If slow electromechanical teleprinters are used, one-and-one half or two stop bits are required.

Conventional notation[edit]

The data/parity/stop (D/P/S) conventional notation specifies the framing of a serial connection. The most common usage on microcomputers is 8/N/1 (8N1). This specifies 8 data bits, no parity, 1 stop bit. In this notation, the parity bit is not included in the data bits. 7/E/1 (7E1) means that an even parity bit is added to the 7 data bits for a total of 8 bits between the start and stop bits. If a receiver of a 7/E/1 stream is expecting an 8/N/1 stream, half the possible bytes will be interpreted as having the high bit set.

Flow control[edit]

In many circumstances a transmitter might be able to send data faster than the receiver is able to process it. To cope with this, serial lines often incorporate a 'handshaking' method, usually distinguished between hardware and software handshaking.

Hardware handshaking is done with extra signals, often the RS-232 RTS/CTS or DTR/DSR signal circuits. Generally, the RTS and CTS are turned off and on from alternate ends to control data flow, for instance when a buffer is almost full. DTR and DSR are usually on all the time and, per the RS-232 standard and its successors, are used to signal from each end that the other equipment is actually present and powered-up. However, manufacturers have over the years built many devices that implemented non-standard variations on the standard, for example, printers that use DTR as flow control.

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Software handshaking is done for example with ASCIIcontrol charactersXON/XOFF to control the flow of data. The XON and XOFF characters are sent by the receiver to the sender to control when the sender will send data, that is, these characters go in the opposite direction to the data being sent. The circuit starts in the 'sending allowed' state. When the receiver's buffers approach capacity, the receiver sends the XOFF character to tell the sender to stop sending data. Later, after the receiver has emptied its buffers, it sends an XON character to tell the sender to resume transmission. It is an example of in-band signaling, where control information is sent over the same channel as its data.

The advantage of hardware handshaking is that it can be extremely fast; it doesn't impose any particular meaning such as ASCII on the transferred data; and it is stateless. Its disadvantage is that it requires more hardware and cabling, and these must be compatible at both ends.

The advantage of software handshaking is that it can be done with absent or incompatible hardware handshaking circuits and cabling. The disadvantage, common to all in-band control signaling, is that it introduces complexities in ensuring that a) control messages get through even when data messages are blocked, and b) data can never be mistaken for control signals. The former is normally dealt with by the operating system or device driver; the latter normally by ensuring that control codes are 'escaped' (such as in the Kermit protocol) or omitted by design (such as in ANSI terminal control).

If no handshaking is employed, an overrun receiver might simply fail to receive data from the transmitter. Approaches for preventing this include reducing the speed of the connection so that the receiver can always keep up; increasing the size of buffers so it can keep up averaged over a longer time; using delays after time-consuming operations (e.g. in termcap) or employing a mechanism to resend data which has been corrupted (e.g. TCP).

'Virtual' serial ports[edit]

A virtual serial port is an emulation of the standard serial port. This port is created by software which enable extra serial ports in an operating system without additional hardware installation (such as expansion cards, etc.). It is possible to create a large number of virtual serial ports in a PC. The only limitation is the amount of resources, such as operating memory and computing power, needed to emulate many serial ports at the same time.

Virtual serial ports emulate all hardware serial port functionality, including baud rate, data bits, parity bits, stop bits, etc. Additionally, they allow controlling the data flow, emulating all signal lines (DTR, DSR, CTS, RTS, DCD, and RI) and customizing pinout. Virtual serial ports are common with Bluetooth and are the standard way of receiving data from Bluetooth-equipped GPS modules.

Virtual serial port emulation can be useful in case there is a lack of available physical serial ports or they do not meet the current requirements. For instance, virtual serial ports can share data between several applications from one GPS device connected to a serial port. Another option is to communicate with any other serial devices via internet or LAN as if they are locally connected to computer (serial over LAN/serial-over-Ethernet technology). Two computers or applications can communicate through an emulated serial port link. Virtual serial port emulators are available for many operating systems including MacOS, Linux, NetBSD and other Unix-like operating systems, and various mobile and desktop versions of Microsoft Windows.

See also[edit]

• ITU-T/CCITT V.24 [de]
• ITU-T/CCITT V.28 [de]

References[edit]

1. ^Webopedia (2003-09-03). 'What is serial port? - A Word Definition From the Webopedia Computer Dictionary'. Webopedia.com. Retrieved 2009-08-07.
2. ^'Serial Cable Connection Guide'. CISCO. 2006-08-01. Retrieved 2016-01-31.
3. ^'RS232 - DTE and DCE connectors'. Lantronix. 2006-03-29. Retrieved 2016-01-31.
4. ^Yost Serial Device Wiring Standard
5. ^Ögren, Joakim. 'Serial (PC 9)'.
6. ^ ^abCyclom-Y Installation Manual, page 38, retrieved on 29 November 2008^{[permanent dead link]}
7. ^'RJ-45 8-Pin to Modem (ALTPIN option)'. Digiftp.digi.com. Retrieved 2014-02-08.
8. ^National Instruments Serial Quick Reference Guide, February 2007
9. ^'RJ-45 10-Pin Plug to DB-25 Modem Cable'. Digiftp.digi.com. Retrieved 2014-02-08.
10. ^Hardware Book RS-232D
11. ^RS-232D EIA/TIA-561 RJ45 Pinout
12. ^'OptiPlex XE Powered Serial Port Configuration'(PDF).
13. ^'Powered Serial Cards - Brainboxes'.
14. ^'HOWTO: Specify Serial Ports Larger than COM9'. Microsoft support. Retrieved 2013-10-26.
15. ^'Paul's 8051 Code Library, IDE Hard Drive Interface'. Pjrc.com. 2005-02-24. Retrieved 2014-02-08.
16. ^'IDE Hard Disk experiments'. Hem.passagen.se. 2004-02-15. Archived from the original on 2004-04-15. Retrieved 2014-02-08.Cite uses deprecated parameter dead-url= (help)
17. ^'The Solution for Seagate 7200.11 HDDs - Hard Drive and Removable Media issues - MSFN Forum'. Msfn.org. Retrieved 2014-02-08.
18. ^'Fixing a Seagate 7200.11 Hard Drive'. Sites.google.com. Retrieved 2014-02-08.
19. ^Serial Port Driver Interfaces; MSDN Microsoft.
20. ^'DCB Structure'. MSDN. Microsoft. Retrieved 2011-03-15.

Further reading[edit]

• Serial Port Complete: COM Ports, USB Virtual COM Ports, and Ports for Embedded Systems; 2nd Edition; Jan Axelson; Lakeview Research; 380 pages; 2007; ISBN978-1-931-44806-2.

External links[edit]