Microprocessor fault log

A microprocessor fault logging arrangement includes means for detecting hardware and software faults 3, 4, 8, which produce an interrupt signal which is applied to the non-maskable interrupt input NMI of microprocessor 1 and, via delay 5, to the RESET input of microprocessor 1. The NMI input causes microprocessor 1 to store the state of selected system parameters in a log of fault records stored in non-volatile memory 2, the selected parameters being stored for fault analysis each time an NMI input signal is generated. The delay 5 allows sufficient time for the selected parameters to be stored in the memory 2 before the microprocessor is reset.