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Polling Serial Devices From the IBM Personal Computer

IP.com Disclosure Number: IPCOM000037189D
Original Publication Date: 1989-Nov-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Dang, MH: AUTHOR [+4]

Abstract

Disclosed is a method for polling devices attached to the IBM Personal Computer (PC) serial port, such as the ROLMphone* 244PC.

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This is the abbreviated version, containing approximately 74% of the total text.

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Polling Serial Devices From the IBM Personal Computer

Disclosed is a method for polling devices attached to the IBM Personal Computer (PC) serial port, such as the ROLMphone* 244PC.

When using an asynchronous communications port to poll a device, the speed of the communications (baud rate) must be set. Conventional applications automatically set (or let the user set) the baud rate and they keep that baud rate constant when polling the device. One example of this scenario is a software application polling a ROLMphone 244PC for telephone status and calling name display updates.

When the PC is not fast enough to handle high baud rates, the software application either reports the problem to the user or ignores the problem and shows erronous results.

With the method discussed here, the application could detect such a problem and automatically take corrective action.

The problem described is reported by the PC UART (Universal Asynchronous Receiver Transmitter) as an overrun error. The UART can be set to interrupt the application when the problem occurs, or the application can occasionally question the UART whether an overrun error has occured.

When the application detects the error, it automatically lowers the polling baud rate to the next lower rate (for example from 9600 to 4800 bits per second). If this does not fix the problem, a lower rate is selected until an error-free rate is reached or until the lowest baud rate is reached.

Typically, the problems will go away...