The name for the COM port started with the original IBM PC. IBM had called the four well-defined communication RS-232 ports the "COM" ports, starting from COM1 through COM4. In BASICA and PC DOS you can open these ports as "COM1:" through "COM4:", and all PC compatibles using MSDOS used the same denotation.[citation needed] Most PC-compatible computers in the 1980s and 1990s had one or two COM ports.
By 2007, most computers shipped with only one or no physical COM ports. Today, few consumer-grade PC-compatible computers include COM ports,[3] though some of them do still include a COM header on the motherboard.[4]
After the RS-232 COM port was removed from most consumer-grade computers, an external USB-to-UART serial adapter cable was used to compensate for the loss. A major supplier of these chips is FTDI.[citation needed]
I/O addressesEdit
The COM ports are interfaced by an integrated circuit such as 16550 UART. This IC has seven internal 8-bit registers which hold information and configuration data about which data is to be sent or was received, the baud rate, interrupt configuration and more. In the case of COM1, these registers can be accessed by writing to or reading from the I/O addresses 0x3F8 to 0x3FF.
If the CPU, for example, wants to send information out on COM1, it writes to I/O port 0x3F8, as this I/O port is "connected" to the UART IC register which holds the information that is to be sent out.
The COM ports in PC-compatible computers are typically defined as[citation needed]:
^"Motherboard Port Guide: Solving Your Connector Mystery". Retrieved 2020-09-14.
Further readingEdit
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 linksEdit
Wikimedia Commons has media related to RS-232 and DE-9 connectors.
How to Interface Hardware in COM ports
October 17, 2023
hardware, interface, communication, port, original, still, common, name, serial, port, interface, compatible, computers, refer, only, physical, ports, also, emulated, ports, such, ports, created, bluetooth, adapters, port, connector, contents, history, address. COM communication port 1 2 is the original yet still common name of the serial port interface on PC compatible computers It can refer not only to physical ports but also to emulated ports such as ports created by Bluetooth or USB adapters COM port DE 9 connector Contents 1 History 2 I O addresses 3 Implementations 4 See also 5 References 6 Further reading 7 External linksHistory EditThe name for the COM port started with the original IBM PC IBM had called the four well defined communication RS 232 ports the COM ports starting from COM1 through COM4 In BASICA and PC DOS you can open these ports as COM1 through COM4 and all PC compatibles using MSDOS used the same denotation citation needed Most PC compatible computers in the 1980s and 1990s had one or two COM ports By 2007 most computers shipped with only one or no physical COM ports Today few consumer grade PC compatible computers include COM ports 3 though some of them do still include a COM header on the motherboard 4 After the RS 232 COM port was removed from most consumer grade computers an external USB to UART serial adapter cable was used to compensate for the loss A major supplier of these chips is FTDI citation needed I O addresses EditThe COM ports are interfaced by an integrated circuit such as 16550 UART This IC has seven internal 8 bit registers which hold information and configuration data about which data is to be sent or was received the baud rate interrupt configuration and more In the case of COM1 these registers can be accessed by writing to or reading from the I O addresses 0x3F8 to 0x3FF If the CPU for example wants to send information out on COM1 it writes to I O port 0x3F8 as this I O port is connected to the UART IC register which holds the information that is to be sent out The COM ports in PC compatible computers are typically defined as citation needed COM1 I O port 0x3F8 IRQ 4 COM2 I O port 0x2F8 IRQ 3 COM3 I O port 0x3E8 IRQ 4 COM4 I O port 0x2E8 IRQ 3Implementations Edit nbsp USB to RS 232 adapter with one 9 pin COM port FTDI US 232R nbsp PCI E card with one 9 pin COM port nbsp PCI card with two 9 pin COM ports nbsp ISA card with one 25 pin COM portSee also EditDevice file Parallel portReferences Edit Configuring a communication port IBM Lotus Domino and Notes Information Center August 14 2008 Archived from the original on 17 September 2013 Stephen Byron Cooper What Is a Com1 Port Retrieved 2021 09 30 Serial port Retrieved 2020 09 14 Motherboard Port Guide Solving Your Connector Mystery Retrieved 2020 09 14 Further reading EditSerial Port Complete COM Ports USB Virtual COM Ports and Ports for Embedded Systems 2nd Edition Jan Axelson Lakeview Research 380 pages 2007 ISBN 978 1 931 44806 2 External links Edit nbsp Wikimedia Commons has media related to wbr RS 232 and wbr DE 9 connectors How to Interface Hardware in COM ports Retrieved from https en wikipedia org w index php title COM hardware interface amp oldid 1174023349, wikipedia, wiki, book, books, library,
