When measuring the voltage on pins of an ADuC7061 that are configured as digital inputs with internal pull-up enabled (the default for many pins after Reset), I'm observing values between 1.8 to 2V, depending on the DMM/oscilloscope used, while DVDD is at 2.5V. Given the input resistance of the voltmeters, this suggests a value of a few MΩ of the internal pull-up resistor.
I suppose this is what I should expect; the answer to a question regarding the ADuC7023 most likely applies to the ADuC706x as well: https://ez.analog.com/message/70967
I'm using the ADuC7061 as an SPI-Slave connected to an SPI master via an ADuM241E isolator. What I want to make sure is, that after an ADuC7061's software reset (fixing er007) the MISO pin will be at 'H' level even for the short duration when it still is a digital input, so that the SPI master -- unaware of the ADuC7061's reset -- can recognize this condition by reading all bits as '1'.
Will the internal, weak pull-up resistor of an ADuC7061's MISO pin (when still configured as a digital input) be enough to guarantee a logic high at the ADuM241's input? This device has a logic high threshold VIH of 0.7xVDDx, in this case 1.75V. The data sheet says, the isolator's maximum input current II per channel may be 10µA. On an ADuC7061's input pin I have observed a current of ≈10µA at a voltage of around 1.6V – which would be below the ADuM241's VIH.
Is it correct that under this conditions an external, stronger pull-up resistor on the MISO line is required?
I would recommend, specifically in harsh real world environments to have a external pull-up!!!