 During the scan process, the input scan normally records the inputs before the program scan and the output scan normally updates the outputs after the program scan. For time-critical applications, immediate input and immediate output instructions are used to interrupt the normal program scan to update the current input or output image table. Immediate instructions are addressed with the file, rack and slot numbers separated by a decimal with the word to be updated. As the program is executed and reaches an immediate input instruction, the scan is interrupted and the bits of the addressed word are updated. The immediate output instruction operates similar to the immediate input instruction. As the scan is interrupted, the bits of the addressed word are updated and the field outputs are energized or de-energized according to the output image table. After the immediate instructions are executed, normal program scan resumes.