Page 55 - Engineering Digital Design

26 CHAPTER 1 / INTRODUCTORY REMARKS AND GLOSSARY

Saturation mode: the physical state of a BIT in which collector current is permitted to
flow.
Schmitt trigger: an electronic gate with hysteresis and high noise immunity that is used
to "square up" pulses.
Selector module: a device whose function it is to steer one of two input signals to either
one of two outputs depending on whether a specific input is active or inactive.
Self-correcting counter: a counter for which all states lead into the main count sequence
or routine.
Sequence detector (recognizer): a sequential machine that is designed to recognize a
particular sequence of input signals.
Sequential machine: any digital machine with feedback paths whose operation is a func-
tion of both its history and its present input data.
Set: a logic 1 condition or an input to a logic device that sets it to a logic 1 condition.
Setup time: the interval of time prior to the transition point during which all data inputs
must remain stable at their proper logic level to ensure that the intended transition will
be initiated.
S-hazard: a static hazard.
Shift register: a register that is capable of shifting operations.
Shift: the movement of binary words to the left or right in a shifter or shift register.
Shifter: a combinational logic device that will shift or rotate data asynchronously upon
presentation.
Sign bit: a bit appended to a binary number (usually in the MSB position) for the purpose
of indicating its sign.
Sign-complement arithmetic: 1's or 2's complement arithmetic.
Sign-magnitude representation: a means of identifying positive and negative binary
numbers by a sign and magnitude.
Single transition time (STT): a state-to-state transition in an asynchronous FSM that
occurs in the shortest possible time, that is, without passing through a race state.
SIPO: serial-in/parallel-out operation mode of a register.
SISO: serial-in/serial-out operation mode of a register.
Slice: that part of a circuit or device that can be cascaded to produce a larger circuit or
device.
Small-scale integration: 1C chips that, by one convention, contain up to 20 gates.
SOP: sum-of-products.
SOP hazard: a static 1-hazard.
Source: one of three terminals of a MOSFET. The origin of a digital signal.
Spill bit: the bit in a shifter or shift register that is spilled off (lost) in a shifting operation.
SPDT switch: single-pole/double-throw switch.
SPST switch: single-pole/single-throw switch.
Square wave: a rectangular waveform.
SRAM: static RAM.
SSI: small-scale integration.
Stability criteria: the requirements that determine if an asynchronous FSM, operated in
the fundamental mode, is stable or unstable in a given state.
Stable state: any logic state of an asynchronous FSM that satisfies the stability criteria.
Stack format: a three-dimensional array of conventional fourth-order K-maps used for
function minimization of more than four variables.