Pc Serial Port Buffer Size - cn-progs96’s blog

Dual-booting all versions of Windows and Linux

Here: Home Legacy 9x Tweaks Modem Net Tweaks

PORT SPEED MAXIMUM SPEED

Select the best Com Port speed and modem Maximum speed

The Serial COM Port is a physical link between the modem and the PC.

The default is far too low and slows downloading.

Select a much higher setting.

The Maximum speed is the modem-to-computer speed, and has an increased data load.

Select the highest available Maximum speed setting - provided you do not have a serious phone line noise problem.

PORT

The SERIAL COM PORT

The Port is a link between modem and computer. There are normally two Serial COM Ports which allow external devices to be connected to the computer. Internal modems have their own integrated Port. Each Port has a speed that can be set independently. The Windows 95/98 default speed for all Serial Ports is just 9,600 bit per second - unacceptably low for a modern modem.

Arriving data is temporarily stored in the Port s FIFO buffer until collected by the CPU and delivered into main memory.

Overruns: If the Port speed is set too high then a busy CPU may not be able to empty the Port s FIFO data buffer before new data arrives there, and you may get a dangerous pile-up Overruns of data which gets damaged - that data will have to be resent. Also if set very high there may be no gain because there may not be sufficient new data in the arriving stream of data. Modern CPUs cope quite well with high Port speeds but some hardware items, video in particular, steal extra CPU time and cause Overruns to occur. Check by enabling the modem log.

If it is set too low then obviously the whole data transfer process will slow down - you will jog cautiously when you could sprint safely.

top of page

PORT SPEED

Suggested Serial COM Port settings:

9,600 modem: select 9,600 bits per second

14,400 modem: select 19,200 bps

19,200 modem: select 38,400 bps

28,800 modem: select 57,600 bps

33,600 modem: select 57,600 bps or try 115,200 bps

faster modem: select 115,200 bps or 230,400 bps

If you do not have a 16550 serial port then try 38,400. You can check which Port type you have by running msd.exe from DOS.

Most often it is best to Disable the Only connect at this speed - when the line connection is poor the modem will connect at a lower speed and will, hopefully, protect against some disconnections.

TUNE THE PORT SETTING 1 All Users

Change the Port setting in Device Manager

1. Select Start Settings Control Panel

2. Open System Device Manager Ports

3. Double-click the COM Port your modem is connected to

4. Select Port Settings

5. Select the new Port speed Bits per second

6. read Other Important Settings - next

7. Click OK

TUNE THE PORT SETTING 2 All Users

While in Port Settings in Device Manager make sure you have these:

Data bits 8

Parity None

Stop bits 1

Flow control Hardware

Click on Advanced

Enable Use FIFO buffers presuming you have FIFO

Put the Receive and Transmit Buffer to maximum right. These control your FIFO buffer - if you have any problems, try reducing the Receive Buffer.

Click OKs to exit

TUNE THE PORT SETTING 3 Intermediate Users

PORT BUFFER - ONLY if you use your modem in MS-DOS mode

You can ignore this setting if you use your modem only under Windows and that s virtually all of us.

Under MS_DOS mode Real, or True, DOS the port buffer size is too small but remember its size under a DOS prompt is the same as for Windows.

The size of buffer allocated in DOS mode can be adjusted in System.ini

Open System.ini.

In the 386Enh section

Add the new lines first line has nothing after the

COMxProtocol

COMxBuffer nnnn

where x represents the COMM Port number used by your modem

and nnnn is the new buffer size usually 2048, perhaps 4096 e.g.

386Enh

COM2Protocol

COM2Buffer 2048

If your link is normally slow, then you probably do not need to make the alteration.

INTERNAL MODEMS Advanced Users

Internal Modems

You may be able to increase the port speed beyond 115,200 bps. Many 33.6 and 56 Kbps internal modems have an in-built UART buffer that can exceed this limit.

Forcing such high speeds is not generally recommended. At best the gain will be marginal, and it may be the cause of Overruns where none previously existed. It may, however, be worthwhile for owners of a 56K modem with a clear phone line.

You edit Win.ini.

Select Start Run; Type in notepad windows win.ini, and click OK.

Scroll down to the Ports section, and edit in or add:

Example: If the modem is installed on COM3, edit in this line:

COM3: 230400,n,8,1,p

Where: 230400 is the port speed in bps

n,8,1 is a standard parity setting you could try E,7,1

p turns the hardware flow control ON - change to x for OFF

Now Save, and Exit Notepad. Options may include 230400, 460800 or 921600 bps

. First backup win.ini from _: Windows. Also watch out for Buffer Overruns.

OTHER TIPS All Users

Highest Speed: You can try for the highest speed that does not cause Buffer Overruns. As a precaution you should use System Monitor to check for any problems, and drop your FIFO Receive buffer in Modems Properties Connection Port Settings and/or the Port speed if they occur. You may also have to reduce it if your ISP, your phone line, or your telephone exchange is misbehaving. Read further explanations in Modems Menu.

External Modems COM2

You should try to use COM2 if you have an external modem.

COM Ports are a low priority call for the CPU which has many more important duties. However the CPU gives slightly higher priority to COM2 than to COM1.

Internal Modems

Remember that in addition to being installed in Device Manager, internal modems should also be installed and configured in the Modems option in Control Panel.

Overruns and Video Cards Advanced Users

Sometimes a Matrox Millennium or other Video Card may keep the CPU too busy to service the FIFO buffer adequately with resulting data Overruns never experienced with this Site s MGA card. Altering its call priority in system.ini will allocate more CPU time to the Port s FIFO buffer. A slight deterioration in Video performance can be expected..Try ONLY if you have Overruns.

For a MGA card: Open system.ini in Notepad and below the 386Enh section add:

mga.drv

PCIChipSet 1

MODEM MAXIMUM SPEED

Your modem talks modem-to-ISPmodem - this is the connection speed, e.g. a V.90,

33.6Kbps or 28.8Kbps modem. It represents the best speed at which it can ever communicate with your ISP s modem along the phone line.

Your modem also talks modem-to-computer - this is the Maximum speed, and appears in two places in Windows 95/98 - in DUN, and in Control Panel. It is advisable to change both, and use the same value in both.

Compressed data is usually decompressed at the receiving modem, and the now larger amount of data is sent thru to the computer. Therefore the Maximum Speed needs to be substantially faster that the connection speed just to keep up.

The limitations placed on Maximum speed are the speed supported by the COM Port, and the CPU speed of the computer. Windows 95/98 selects a very conservative default speed so that slower computers do not lose data during transfers. Increase it.

TUNE MAXIMUM SPEED in DUN 1 All Users

Change the Maximum Speed in DUN

Select My Computer Dial-Up Networking

Right-click your Network Server icon, and select Properties

Using the General tab sheet, select the highest Maximum speed available

Disable Only connect at this speed - to allow connection at a lower speed when required.

Click the OKs until out.

ALSO CHANGE IT IN MODEMS 2 All Users

Also change the Maximum Speed in Modems

Select Start Settings Control Panel Modems

Double-click the Modems icon

Using the General Tab sheet, choose your modem from the list, and click the Properties button

In the next General tab sheet scroll down and select the same Maximum speed you used in Dial-up Networking. Click OK

Disable Only connect at this speed - to allow connection at a lower speed when required

Click OK and then Close

Note: Even with Only connect at this speed disabled, you may, at times, have to reduce the Maximum speed in order to maintain a good connection - if so, then your downloading will suffer, and you should discuss this with your ISP while you check your settings, your phone line, and are investigating other ISPs..

Please remember that you alone are responsible for the consequences of any changes you make to your computer hardware or software.

TweakHomePC

Visual Basic interfacing RS-232, MODERM dial-up phone and I2C serial communications. pc interface hardware electronic and control input output hardware.

In computing, a serial port is a serial communication physical interface through which information transfers in or out one bit at a time in contrast to a parallel.

Pira CZ Remote COM Port: Freeware application which allows to control any RS232 device via TCP/IP network LAN, internet. The application supplies hardware based.

Nov 18, 2014 I m guessing your serial port s FIFO is limited to 16 bytes. 1. Run receive before running send perhaps you are - I can t tell. 2. Modify receive to read.

Table of contents, Sheepdog s Serial Port Page: Ads from sponsor brief, please read.. Hardware issues of using serial port Software what you put in a program.

Serial I/O Routines Using the 8051 s Built-In UART This 8051 code library is intended to provide a variety of commonly used I/O functions found in high-level.

A male DE-9 connector used for a serial port on an IBM PC compatible computer along with the serial port symbol. Pinout

In computing, a serial port is a serial communication physical 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 more or less compliant to the RS-232 standard, intended to interface with a modem or with a similar communication device.

Modern computers without serial ports may require serial-to-USB 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.

Contents

1 Hardware

1.1 DTE and DCE

1.2 Connectors

1.3 Pinouts

1.4 Hardware abstraction

2 Common applications for serial ports

3 Settings

3.1 Speed

3.2 Data bits

3.3 Parity

3.4 Stop bits

3.5 Conventional notation

3.6 Flow control

4 Virtual serial ports

5 See also

6 References

7 Further reading

8 External links

Hardware edit

A PCI Express 1 card with one serial port

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 or microcomputer 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.

Connectors edit

Pair of female Mini DIN-8 connectors used for RS-422 serial ports on a Macintosh LC computer

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 that was similarly changed from the original Centronics-style 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.

A Hirose 3560-16S used for RS-232 on a Tatung TWN-5213 CU tablet computer. Below is a mating 3540-16P-CV connector.

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.

The standard specifies 20 different signal connections. Since most devices use only a few signals, smaller connectors can often be 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. Standard EIA/TIA 561 specifies a pin assignment, but the Yost Serial Device Wiring Standard 2 invented by Dave Yost and popularized by the Unix System Administration Handbook is common on Unix computers and newer devices from Cisco Systems. Many devices don t use either of these standards. 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. 3

Signal

Origin

DB-25

DE-9

TIA-574

MMJ

8P8C RJ45

10P10C RJ50

Name

Abbreviation

DTE

DCE

EIA/TIA-561

Yost DTE

Yost DCE

Cyclades 4

Digi ALTPIN option 5

National Instruments 6

Digi 7

Transmitted Data

TxD

Received Data

RxD

Data Terminal Ready

DTR

Data Carrier Detect

DCD

N/A

Data Set Ready

DSR

Ring Indicator

Request To Send

RTS

Clear To Send

CTS

Signal Ground

common

3,4

4,5

Protective Ground

The signals are named from the standpoint of the DTE, for example, an IBM-PC compatible serial port. The ground signal 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. Connecting this to pin 7 signal reference ground is a common practice but not essential.

Note that EIA/TIA 561 combines DSR and RI, 8 9 and the Yost standard combines DSR and DCD.

A converter from USB to an RS-232 compatible serial port; more than a physical transition, it requires a driver in the host system software and a built-in processor to emulate the functions of the IBM XT compatible serial port hardware.

Hardware abstraction edit

Operating systems usually use a symbolic name to refer to the serial ports of a computer. Unix-like operating systems usually label the serial port devices /dev/tty TTY is a common trademark-free abbreviation for teletype where represents a string identifying the terminal device; 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 Microsoft MS-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. 10

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.

Some CNC controllers

Uninterruptible power supply

Stenography or Stenotype machines.

Software debuggers that run on a second computer.

Industrial field buses

Printers

Computer terminal, teletype

Older digital cameras

Networking Macintosh AppleTalk using RS-422 at 230.4 kbit/s

Serial mouse

Older GSM mobile phones

Some Telescopes

IDE hard drive 11 12 repair 13 14

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, battery low alarm 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

A four-port serial RS-232 PCI Express 1 expansion card with an octopus cable that breaks the card s DC-37 connector into four standard DE-9 connectors

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 can not 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 bauds. 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. 15 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

Main article: Parity bit

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 none N, odd O, even E, mark M, or space S. None means that no parity bit is sent at all. Mark parity means that the parity bit is always set to the mark signal condition logical 1 and likewise space parity always sends the parity bit in the space signal condition. Aside from uncommon applications that use the 9th parity bit for some form of addressing or special signalling, 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 D/P/S Data/Parity/Stop 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 seven data bits for a total of eight 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

Main article: Flow control data

A serial port may use signals in the interface to pause and resume the transmission of data. For example, a slow printer might need to handshake with the serial port to indicate that data should be paused while the mechanism advances a line.

Common hardware handshake signals hardware flow control use 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.

Another method of flow control software flow control uses special characters such as XON/XOFF to control the flow of data. The XON/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. These are non-printing characters and are interpreted as handshake signals by printers, terminals, and computer systems.

XON/XOFF flow control is an example of in-band signaling, in which control information is sent over the same channel used for the data. XON/XOFF handshaking presents difficulties as XON and XOFF characters might appear in the data being sent and receivers may interpret them as flow control. Such characters sent as part of the data stream must be encoded in an escape sequence to prevent this, and the receiving and sending software must generate and interpret these escape sequences. On the other hand, since no extra signal circuits are required, XON/XOFF flow control can be done on a 3 wire interface.

Virtual serial ports edit

Main article: COM port redirector

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/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, and various mobile and desktop versions of Microsoft Windows.

Optimize Internet downloads by changing the Serial COM Port speed for your own modem - speed boosts for PC computer system and Windows ME SE 98 95.

Sending Files. Here are two helpful little methods for sending files through the serial port. Of course, these are the bare essentials and as always, you should check.