Browse Prior Art Database

Communications Port Detection in a Personal Computer

IP.com Disclosure Number: IPCOM000037191D
Original Publication Date: 1989-Nov-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 3 page(s) / 41K

Publishing Venue

IBM

Related People

Dang, MH: AUTHOR [+4]

Abstract

Disclosed is a method to accurately determine if a communications port is installed in an IBM Personal Computer (PC) or Personal System/2* (PS/2) computer, in both OS/2* and DOS system environments.

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Communications Port Detection in a Personal Computer

Disclosed is a method to accurately determine if a communications port is installed in an IBM Personal Computer (PC) or Personal System/2* (PS/2) computer, in both OS/2* and DOS system environments.

In the IBM PC and PS/2 computers communications (comm) ports are located at fixed addresses. For example, comm port 1 occupies the input/output address range 03F8H to 03FFH. This address range provides access to the Universal Asynchronous Receiver Transmitter (UARTs) registers. To determine if a comm port is installed, the application could look at that port's fixed address and test for behavior specific only to UARTs. The following describes characteristics unique to the UARTs used in the IBM PC or PS/2 computers. These PCs use the NS8250, NS16450, NS16550, or compatible UARTs. The first two registers of the UART have a dual function: 1. Register 1 is the transmitter/receiver register, and

register

2 is the interrupt enable register, or

2. The pair act as the baud rate divisor.

The function of these two registers is determined by the value of bit 7 in the UART Line Control Register (LCR). If this bit is set to one, the first two registers act as a baud rate divisor; otherwise, they act as transmitter/receiver and interrupt enable registers.

To determine the presence of a UART, applications perform the following steps: 1. Set bit 7 of the Line Control Register (LCR) to 1.

2. Output a certain number (say 0030h) to th...