An introduction to speed independent circuit theory

Abstract

In the study of switching systems, the timing of the circuits is often of great importance. In a computer, for example, one imposes a certain sequencing of information through the computer circuits to obtain a desired calculation. Sometimes more than one operation can be performed simultaneously, or in parallel; and by so doing, the total calculation time may be reduced. Various ways have been used to insure proper timing in the circuits. A computer may have a basic clock pulse which is imposed on the circuits to synchronize the operations. A combinational circuit may be designed without considering timing. The time requred for the circuit to operate under the worst allowable tolerance conditions can then be calculated; and a suficient number of clock pulses can then be assigned to this circuit, between input and output, such that the circuit can attain the correct output before it is sent to another circuit. Aother method of timing, generally called asynchronous, is to provide completion signals in the computer for each operation. This completion signal, or "reply back", is used to turn off the operation. The turn off then provides another signal to initiate the next operation. These extra internal signals provide the necessary circuit timing, and no external clock is requred.