Browse Prior Art Database

Off-The-Wall Data Communications

IP.com Disclosure Number: IPCOM000034561D
Original Publication Date: 1989-Mar-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 58K

Publishing Venue

IBM

Related People

Barker, JW: AUTHOR [+5]

Abstract

This article describes a data communications link which will automatically switch between a hard-wired data link and a portable battery-powered radio link. A support terminal which comprises a battery-powered computer requires data communications with a host for proper operation. When the terminal is "on the wall", it will recharge its batteries and can also communicate with the host computer, as illustrated in block diagram in Fig. 1. When the terminal is later used in a portable mode, communications must automatically switch to a battery-powered radio link, as illustrated in Fig. 2. This is accomplished by sensing an "off-the-wall" (OTW) signal which is controlled by a jumper in the hard-wired connector. (Image Omitted) Fig. 3 shows the OTW detection circuitry.

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Off-The-Wall Data Communications

This article describes a data communications link which will automatically switch between a hard-wired data link and a portable battery-powered radio link. A support terminal which comprises a battery-powered computer requires data communications with a host for proper operation. When the terminal is "on the wall", it will recharge its batteries and can also communicate with the host computer, as illustrated in block diagram in Fig. 1. When the terminal is later used in a portable mode, communications must automatically switch to a battery- powered radio link, as illustrated in Fig. 2. This is accomplished by sensing an "off-the-wall" (OTW) signal which is controlled by a jumper in the hard-wired connector.

(Image Omitted)

Fig. 3 shows the OTW detection circuitry. The OTW line is connected to an input of a programmable peripheral interface (PPI). This signal is pulled to supply voltage Vcc through a resistor so that it is read as a logical "1" when the communications cable is not attached to the wall connector (i.e., OTW). When the communications cable is attached to the wall connector, the jumper inside the wall connector connects the OTW line to ground (logical "0") which indicates via I/O read that the connector is indeed attached to the wall. The communications device driver reads the state of this signal in order to decide which data link is available. Fig. 4 is a block diagram of the terminal link system.

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