Hello Hcag, Generally, the port impedance will change dynamically by voltage and current. There is information of the I/O characteristics(VOH/L vs IOH/L) of the RL78 on Renesas web. But no information of RX63 is there. ( If necessary the characteristic data, contact your supplier. If it goes well, you can get it. ) Now, I tried to measure it with some resistors which are close to me. According to the results, you may consider that as 100ohm ! PORT(PC3 at RX631) VOL/VOH Pull Up/Down Resistor value Pull Up/Down to Port Impedance OUTPUT LOW Vol=1.23V 200ohm POWER(3.3V) Z=119ohm OUTPUT LOW Vol=0.34V 766ohm POWER(3.3V) Z=88ohm OUTPUT HIGH Voh=1.85V 200ohm GND Z=157ohm OUTPUT HIGH Voh=2.87V 766ohm GND Z=115ohm In addition, I see the current/voltage waveform at VIL with 200ohm and 766ohm pullup with capacitor of my Thumb and index finger(20nF?). It is difficult to measure the current and voltage flowing in the capacitor..... Refer:RL78 IOH-VOH characteristics http://www.renesas.com/products/mpumcu/rl78/rl78g1x/rl78g13/child/rl78_char.jsp
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