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Browse Prior Art Database

Automatic Protection Against Erroneous Modem Card Plugging

IP.com Disclosure Number: IPCOM000034627D
Original Publication Date: 1989-Mar-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Bouvier, F: AUTHOR [+5]

Abstract

The new generation of communication controllers offers integrated synchronous modems, in addition to the standard CCITT V24/V35 adapters. Due to the amount of circuits required, only two narrow-band modems 9.6/14.4 bps), or only one wide-band modem (56 kbps), can be housed on a card, while the density of adapters is four adapters per card. Line addressing compatibility between V24/V35 adapters and integrated modems leads to configuration constraints. The wide-band 56 kbps modem card uses four-line addresses, while the twin 9.6/14.4 kbps modem card uses two-line addresses. As a result, a pair of board positions is needed by narrow band modems, but only one board slot by the wide-band card, the remaining position of the pair being lost.

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Automatic Protection Against Erroneous Modem Card Plugging

The new generation of communication controllers offers integrated synchronous modems, in addition to the standard CCITT V24/V35 adapters. Due to the amount of circuits required, only two narrow-band modems 9.6/14.4 bps), or only one wide-band modem (56 kbps), can be housed on a card, while the density of adapters is four adapters per card. Line addressing compatibility between V24/V35 adapters and integrated modems leads to configuration constraints. The wide-band 56 kbps modem card uses four-line addresses, while the twin 9.6/14.4 kbps modem card uses two-line addresses. As a result, a pair of board positions is needed by narrow band modems, but only one board slot by the wide-band card, the remaining position of the pair being lost. Modem cards are housed in physically identical cassettes, and are hot pluggable into the communication controller, which is customer- settable. Erroneous cassette plugging would disturb or break the data communications already established. The address of a modem cassette is defined by its position on the board. A three-bit address bus, wired on the board, defines four pairs of cassette positions. Positions 1 and 2 correspond to lines 0 to 3, positions 2 and 3 correspond to lines 4 to 7, etc. As a wide-band modem uses four-line addresses, when plugged in the even position of a pair, it prohibits the use of the associated odd position. Conversely, when plugged into the odd slot of a pair, the associated even slot cannot be used. As shown in the figure, interlocking between a pair of modem cassettes uses a latch made up of two NAND circuits. The first installed modem has its "busy in" input which is at an up level due to +5 V. When plugged in, a reset signal is generated by an analog timer. At the end of the reset delay, the NAND circuit is activated a...