the corresponding status. The outputs of the AND gates are all OR-wired to generate a single interrupt line that requests attention from the computer. Using the communication interface, the computer can later read the status register to know the cause of the interruption. The computer can disable or enable any sources of interruption by respectively writing '0's and '1's on the mask register. Manufacturers shall equip their instruments with communication interfaces to access the registers remotely, as well as to provide documentation to explain the meaning of all status bits. A good example is the multimeter 3456A, released by HP in 1981 [1], which had an HP-IB interface (the predecessor of GPIB) and possessed an 8-bit status register described as follows: ◗ Bit 7, limits failure: Activated when a limit is exceeded in the pass/fail math operation. ◗ Bit 6, service request: Activated when service is required. ◗ Bit 5, program memory error: Activated when the internal memory space is exceeded. ◗ Bit 4, illegal instrument state/ internal error/ syntax error: Activated when the instrument is unable to