I like your solution about the AND gate but I need to lower the connections.
Can you please elaborate your solution? thxSome uC provide also configurable open drain option for TX pin.
Because it is better in every regard discussed in post#4.why the AND gate based solution is safer than the diode based solution?
I target the maximum possible Baud. Do you have an example of such operation usage?Do you actually target to 3.8 Mbaud? Then bus capacitance is rather critical. I would consider to use no diodes but to enable and disable TX pins, similar to operation of a RS-485 bus.
The firmware must be able to handle half duplex anyway, specifically only send when the bus is idle.I target the maximum possible Baud. Do you have an example of such operation usage?
One of the issue I face is about the MCU firmware that do not gives the capability to enable/disable the TX. I try to design a pure electronic solution tranparent to the MCU (without coding).
Hi,
I doubt that evry microcontroller can work at exactly 3.8MHz. It's not the "max value" that counts ... it's the exact 3.8MHz you have to check.
So 0.25 VCC is the max value your system can tolerate. This is 0.825V
Not IOL is important, but VOL at 1mA.
Maybe you need to look for VOL vs IOL charts. Maybe interpolate from other VOL values.
A BAT54 has about 0.35V at 1mA.
Thus VOL needs to be less than 0.825V - 0.35V = 0.475V (@1mA)
VOL of 1.3V makes no sense at all. It's against all standards I know for 3.3V systems.
Klaus
Thank you FvM.The firmware must be able to handle half duplex anyway, specifically only send when the bus is idle.
Regarding baud rate, it must be achievable for all involved nodes. I'd probably go for a standard baud rate like 921k. At this rate, a low ohmic diode/resistor circuit should still work, e.g. 470 to 1k.
See post #9.If I succeed to get open drain for TX pin, do I still need the diode?
OK, it's clearSee post #9.
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