| 摘要 |
PROBLEM TO BE SOLVED: To provide an input/output unit and its internal data communication method capable of transmitting and receiving surely data between internal devices without an abnormal processing even in an environment influenced by an electrical noise. SOLUTION: A programmable controller 1 can execute data communications with external equipment by execution of serial communications by an MCU 5 and an ASIC 4. When transmitting data mutually to a partner and receiving a NAK signal from the partner, the ASIC 4 and the MCU 5 transmit a heart- beat command. Since the heart-beat command has the shorter data length compared with usual serial data, the command can be transmitted to the partner without being influenced by the electrical noise. Therefore, its own watchdog timer can be cleared by receiving an ACK signal from the transmission partner, and hereby stop of an analog unit 3 caused by the influence of the electrical noise can be prevented.
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