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Control Circuit Bypassing some Flexible Diskette Controller Functions

IP.com Disclosure Number: IPCOM000051714D
Original Publication Date: 1981-Mar-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 37K

Publishing Venue

IBM

Related People

Ott, WB: AUTHOR [+2]

Abstract

This article describes logic for utilizing desired functions of commercially available flexible diskette controllers and bypassing other functions provided by such controllers which are either incompatible with or less desirable to use with a flexible diskette drive. Commercially available flexible diskette controllers interface with diskette drives through an input/output port of the main processor. However, with some diskette drives it is necessary to provide auxiliary control of the controller without disturbing the interface, that being its ability to execute the read/write commands. The additional functions performed by the commercially available flexible diskette controller controls the auxiliary functions of the diskette drive, such as the seek and head load functions.

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Control Circuit Bypassing some Flexible Diskette Controller Functions

This article describes logic for utilizing desired functions of commercially available flexible diskette controllers and bypassing other functions provided by such controllers which are either incompatible with or less desirable to use with a flexible diskette drive. Commercially available flexible diskette controllers interface with diskette drives through an input/output port of the main processor. However, with some diskette drives it is necessary to provide auxiliary control of the controller without disturbing the interface, that being its ability to execute the read/write commands.

The additional functions performed by the commercially available flexible diskette controller controls the auxiliary functions of the diskette drive, such as the seek and head load functions.

Where it is desirable to utilize a commercially available flexible diskette controller to perform only its primary function of executing read/write commands, the circuit shown in the figure may be used to disable the auxiliary commands. In the figure, the flexible diskette controller (FDC) 1 may be any of the commercially available types, such as the NEC 765, the Intel type 8171 or 8172, or the Western Digital type 1771, 1781, 1791 or 1793. Each of these have a common operation in that if the flexible diskette controller fails to find a selected sector after a specific number of index pulses are provided thereto, the controller aborts the command and reports no sector found. However, if the index pulses are blocked from reaching the flexible diskette controller, it will wait indefinitely to complete a command. Therefore, all auxiliary functions can be implemented by a microprocessor with a communication between the microprocessor and the flexible diskette controller limited to just three signals. These are a start read/write operation signal from the controller to the microprocessor, an end of read/write operation signal from the controller to the microprocessor, and an auxiliary function from the busy signal from the microprocessor to the controller....