298 THE PDP-11 FAMILY

A shorter time-out, approximately 100 microseconds, is used to detect a failure in a peripheral after at least one SCLK signal transition has been received. If this limit is reached, the controller asserts EXC to tell the peripheral to disconnect.

The chapter author wishes to acknowledge the patience of J. Craig Mudge, the editor who provided the impetus to produce this chapter, and of Heidi Baldus, who spent a great many hours overseeing the production of this work, many of them on the telephone at a distance of 3000 miles from the author.

Robert Chen and Alice Parker contributed greatly by their detailed reviews of the first draft. Others who helped were Sas Durvasula, Robert E. Stewart, Harold Stone, Mike Riggle and Don Vonada. George Herbster, patent attorney and friend to many engineers, provided reference materials on short notice.

The definitions below are offered as an aid to understanding the technical meaning of some words used in this chapter.

Assert (transitive verb) - to cause a signal to take the "true" or asserted state.

Asserted (nominal) - to be in the "true" state.

Assertion (noun) - the transition from negated to asserted.

Bandwidth (noun) - data transfer rate measured in information units (e.g., bits, bytes, or words) per unit time.

Connection (noun) - an attachment to a bus and the logic and functions of the attached sub system. Synonyms: node, interface.

Interval (noun) - an extent in time. Synonym:

Negate (transitive verb) - to cause a signal to take the "false" or negated state.

Negated (nominal) - to be in the "false" state.

Negation (noun) - the transition from asserted to negated.

Read (transitive verb) - to move data from a register, memory, or secondary storage.

Sense (transitive verb) - to capture data from bus signal lines. Synonyms: receive, gate in, strobe.

Slot (noun) - a particular interval.

Time-out (intransitive verb) - to wait for the end of an interval and to take an action associated with the failure of some event to occur within the interval.

Transfer (transitive verb) - to move data (a data word).

Transmit (transitive verb) - to place data on bus signal lines. Synonyms: drive, gate out.

When (adverb) - at the instant that.

Whenever (adverb) - every time that.

While (adverb) - throughout the interval that.

Write (transitive verb) - to move data into a register, memory, or secondary storage.

For further reading on bus design in general, the following references will provide an entry into some of the published literature.

Blaauw, Gerrit A., Digital System Implementation, Chapter 9, "Communication," Pp 286-3 16; Prentice-Hall (1976). [I/O channel architecture, data synchronization]

Chen, Robert C.H., "Bus Communications Systems," Ph.D. thesis, Department of Computer Science, Carnegie-Mellon University (January 1974). [synchronization, arbitration, and deadlock]

Enslow, Philip H., Jr. (ed.), Multiprocessors and Parallel Processing, Chapter 2, "Systems Hardware," pp. 26-80; Wiley (1974). [Multiprocessor bus organization; Unibus; tradeoffs in bus design; I/O topology]

Ornstein, S.M., W.R. Crowther, M.F. Kraley, R.D. Bressler, A. Michel, and F.E. Heart, "Pluribus - a reliable multiprocessor," A FIPS Conference Proceedings, Vol. 44(1975), National Computer Conference, pp. 55 1-559. [Multiprocessor IMP for A RPA NE7]