Signature Analysis Testing of the Interrupt Controller in a Microprocessor Based System
Original Publication Date: 1983-Feb-01
Included in the Prior Art Database: 2005-Feb-06
Signature analysis is a useful technique for diagnosing problems within microprocessor based products. However, if feedback paths are present, they must be broken so that the true source of a defect can be isolated to a single module. This article describes a set of routines which effectively break up the feedback path between, e.g., an Intel 8085 microprocessor and an Intel 8259 interrupt controller. The feedback mechanism of this circuit is an interrupt request (INTR) going to the 8085 and an interrupt acknowledge (INTA) going from the 8085 to fetch a call instruction from the 8259. Fig. 1 shows such a system along with the additional hardware required to test it as described below. The technique described can be easily extended to other similar microprocessor/interrupt controller combinations.