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How do i read the correct value easier for uPD78P018FY?

Latest Updated:11/01/2001

Question:

To lower the power consumption of the uPD78P018FY, the port mode is set to the input mode and the internal pull-up resistor is enabled only when data needs to be read.
In this case, however, it is difficult to read the correct value.

   MOV  PM1, #**
   MOV  PM2, #**
   MOV  PUO, #**
   MOV  A, P1

Answer:

Even if the internal pull-up resistor is enabled, the resistance value is 40kΩ (90kΩ MAX), so because the charge-up of the capacitor of the pin includes the external wiring capacitance, it takes longer to charge up to high level than the instruction execution time.
As a result, correct values cannot be obtained even when the pull-up resistor is enabled and the port is immediately read.
Suitable Products
RL78 Family
78K Family