On 21.04.2017 12:34, email@example.com wrote: > Although it's caption says: "Port B Output Circuit", which originally > made me believe that it's only the part used when the pin is > configured as output, it also contains a line described as "INPUT > DATA". This line seems to be in fact pulled up. I assume this is what > makes it reliable - a kind of internal pullup. Would still appreciate > corrections if I am missing something here. Hi, CMOS uses push-pull drives, but my impression is that older technologies use pull-ups with open-collector/open-drain drives. I.e. passive up, active down. CMOS can emulate open-drain drive by using an external pull-up resistor and switching between input (high-impedance) and drive-0 states. I have used this often to create I2C using regular IO pins. Microcontrollers often have weak pull-downs or pull-ups. However, resistors in the MOhm range increase the production testing time due to the requirement to measure very small currents, which is a reason they are not always used. (In addition to having a minimal effect in leakage during low-power modes.) -Pasi Message was sent through the cbm-hackers mailing listReceived on 2017-04-21 10:03:07
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