Test and functional diagnosis of digital devices and systems

The necessity in periodic check of test functional diagnostic digital devices and systems containing self-check tools for built-in diagnostics is attributable to the need to detect such faults which do not show up on a specified time interval. A ring-like register is proposed for this purpose whose feedbacks are closed through diagnostics circuits. Structural circuits of devices and systems completely self-checking and selftesting, on a specified time interval are discussed.