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Receiver Speed Select Circuit for R Loop Terminals

IP.com Disclosure Number: IPCOM000086041D
Original Publication Date: 1976-Jul-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 63K

Publishing Venue

IBM

Related People

Hendrickson, TA: AUTHOR

Abstract

Serial loop communications systems may use several transmission data rates on their loops. This provides for remote loop operation and local loop backup operation which utilize IBM or OEM modems. Since these modem data rates may range from 9600 baud to 600 baud, it is highly desirable for the terminals on the associated baseband loop to automatically select the proper data rate to match the modem data rate, thus eliminating manual terminal speed select setups.

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Receiver Speed Select Circuit for R Loop Terminals

Serial loop communications systems may use several transmission data rates on their loops. This provides for remote loop operation and local loop backup operation which utilize IBM or OEM modems. Since these modem data rates may range from 9600 baud to 600 baud, it is highly desirable for the terminals on the associated baseband loop to automatically select the proper data rate to match the modem data rate, thus eliminating manual terminal speed select setups.

A particular loop system transmits a 9600 square-wave baseband signal round its loop. These square-wave pulses are called dibits and are shown in Fig.
A. A data bit may be comprised of 1, 2, 4, 8......N digits.

In addition, the system uses a "phase reversal" in the dibit stream to denote two things; (a) the leading edge boundary of a data bit and (b) a 0 bit. Once the data bit boundary has been established, every Nth dibit can be examined to see if the dibit stream is still in phase with the preceding data bit, or if the phase changed by 18O degrees. If no phase change has occurred the current bit is 1; a phase change indicates the current data bit is a 0. (Note: opposite bit significance could have been used as readily.)

In Fig. 2, it can be noted that the speed can automatically be determined when it is unknown, by simply counting the number of dibits between two adjacent 0 data bits; i.e., between two phase reversals.

The number of dibits between two phase changes (not counting the one in which the phase change occurred) for several speeds are shown in the follo...