| 摘要 |
PURPOSE:To maintain the content of a user program memory even when the CPU of a controller makes uncontrolled run by making a write controlling means permit writing in the program memory only when a programer is connected. CONSTITUTION:When a controller 10 is not connected to a programer 20 and operating independently, a line 24 and a write controlling means 13 are not connected. Accordingly, the input of the write controlling means 13 is made 'H' by positive power source, and input of the inverse of WE terminal becomes 'H' not depending on the inverse of WR signal as the result of logical operation of the write controlling means 13. In this case, writing in EEPROM 12 is prohibited. When the controller 10 is connected to the programer 20, the line 24 and the write controlling means 13 are connected, and accordingly, the input of the write controlling means is made 'L' by grounding. Accordingly, the input of the inverse of WE terminal is changed by the inverse of WR signal as the result of logical operation of the write controlling means, and writing operation becomes possible.
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