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Part Number: TCAN1042-Q1
How does the TXD pin work?
Help me understand (if STB = L) how TXD determines “H or Open” if CAN bus State is recessive. From the description below, it sounds like it will always be H…
TXD is the input of the CAN transceiver that drives messages from the controller to the CAN bus on the CANH and CANL pins. If STB is low, then the device is in normal mode and the CAN bus driver and receiver are fully functioning. The way the TXD pin works is by feeding the signal from the controller into a comparator that determines if the signal is a low or a high based on a reference threshold. Based on this result the comparator then tells the bus drivers circuitry to either drive CANH and CANL (for a low on TXD) or not drive and leave the CAN bus at the recessive level (high on TXD).
The reason an open on TXD is also interpreted as a high by the transceiver is because there is an internal pull-up on TXD that will keep it in a high state if it is not being driven.
Please let me know if that makes sense and if you have any other questions.
Texas Instruments | INT-TRX| Applications Engineer
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In reply to Eric Hackett:
What is the internal pullup resistance value is on this pin?
In reply to Viktorija Cecil:
The typical value of the pull-up resistor is 220k ohms.
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