A transistor is used on pin PD1 of the microcontroller, as seen in Figure 7, to isolate the transmit line. If the transmit pin of the microprocessor was connected directly to the ECU serial line it would be held high when the ECU was trying to bring the line low for communication. Holding the serial line high when inactive is extremely common and used in many serial communication methods. "One design issue with the microcontroller UART is that the transmit pin on the microcontroller is held high when inactive. Here is the explanation from the writeup on the second circuit Could anyone provide some insight into this? I feel like the 2nd circuit is the better way to go but Id rather not if the first one does the same thing more or less somehow.Īlso can anyone explain the oscillator in the circuit below, is it required for the interface or is it simply the clock for the mcu? Here is another interface circuit I found, I'm not sure how both of these circuits could be accomplishing the same thing. Im aware this does not include level shifting from 5v to 3v3 which I believe I just need a suitable level shifter ic to accomplish, my question here is how does this circuit allow 1 wire to 2 wire communication? Wouldn't the diode in that orientation not allow the TX pin to send its data? I believe I've found a suitable way using the following circuit I've been working on a diagnostics program for my old diesel, I need the TX/RX pins of my esp32 to connect to the 1 wire ALDL port.
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