| 摘要 |
An encoder of a process unit encodes an identification code output by the CPU of a main unit, thereby obtaining a response code. The response code is returned to the main unit. The logic of the encoder is changeable. At shipment, a first logic is set in the encoder. After use, a second logic determined on the basis of a predetermined rule is set to the encoder under control of the CPU. The main unit stores the second logic set in the encoder of the process unit. The identification code is encoded by the encoder of the main unit individually with the first logic and the stored second logic, with the result that normal codes are obtained. The normal codes are collated with the response code by a collator. The CPU identifies the status of the process unit based on the result of the collation by the collator.
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