Browse Prior Art Database

Cassette Data Stream Using Programmable Timer

IP.com Disclosure Number: IPCOM000045992D
Original Publication Date: 1983-May-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Milling, PE: AUTHOR

Abstract

Described herein is a method of driving a programmable timer to produce an accurate frequency modulated (FM) data stream for storing data on a cassette tape. In an FM data stream, one frequency is provided for a "0" bit and another frequency is provided for a "l" bit. For instance, 2.0 kHz may represent a logic "l", and l.2 kHz may represent a logic "0". For maximum bit density on a tape, only one complete cycle of the appropriate frequency is recorded per bit.

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Cassette Data Stream Using Programmable Timer

Described herein is a method of driving a programmable timer to produce an accurate frequency modulated (FM) data stream for storing data on a cassette tape. In an FM data stream, one frequency is provided for a "0" bit and another frequency is provided for a "l" bit. For instance, 2.0 kHz may represent a logic "l", and l.2 kHz may represent a logic "0". For maximum bit density on a tape, only one complete cycle of the appropriate frequency is recorded per bit.

One manner of recording a single cycle at the appropriate frequency is through the utilization of a programmable counter timer, such as the Intel 8253. The counter should be set in the square-wave generator mode. Assuming that the input clock frequency is l MHz, then each clock time is l microsecond. If the "0" bit is required, the duration of a single cycle at 2 kHz is 500 microseconds, so the timer's internal counter is programmed to 500. Thus, after 500 microseconds have occurred, one square-wave cycle at a 2 kHz rate will have been provided. If a logic "l" bit is desired, then the period is 832 microseconds, the number 832 is latched into the timer's counter, and an 832-microsecond cycle will be provided.

Referring to the figure, it is important to set the timer's counter approximately half way through one cycle for the next cycle so that the new cycle immediately follows without any time jitter. Resetting the timer's counter approximately half way through...