Innovative Test Solutions for Pin-Limited Microcontrollers

A scan-based test methodology was adopted for the Freescale S08 and RS08 (8-bit) families of microcontrollers (MCUs) several years ago. This methodology has been shown to provide high quality testing and is an important part of Freescale’s “ZeroDefect” initiative. One of the difficult restrictions placed on these families of products is the requirement for applications requiring very few pins. For instance, the 9S08QG8 MCU is available in an 8-pin package, and the 9S08KA2 MCU is available in a 6-pin package. Because of these packaging requirements, several test methods have been developed to implement scan-based testing using very few pins. The methods include full single scan chain testing, an internally-generated reset (no dedicated reset pin), test mode latching with no dedicated test mode pins, IDDQ measurement using a single power supply, an indirect method for verifying correct mode entry, and pin multiplexing that combines several signals required for scan-based testing.