A safety instrument suitable for use in an industrial application includes a logic card having a microcontroller configured to perform self-test of the instrument and surveillance functions of an external system that is monitored and/or controlled by the instrument. The logic card also includes at least one complex programmable logic device (CPLD) configured to execute logic functions relating to human safety requirements of the external system independently of the microcontroller and to provide address decoding, input/output addressing, and/or registers for the microcontroller. The instrument further includes one or more I/O modules that are operatively coupled to the logic card to communicate monitor signals and/or control signals from the logic card to the external system.