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I've searched and searched and can't figure out what this thing is. The trace on the bottom is going to a GPIO pin on a micro controller. The top trace goes out to a serial communications line. As best I can tell, the line is a half-duplex open drain serial connection. I think the comms itself is just bit-banged in the MCU.

Partially out of the image is a 5v zener diode. That Zener is being used as a voltage regulator and is connected to a 47.3k resistor, pulling up the comms line. I'm not sure what the resistor between the comms and the second line on the IC is doing, nor the other resistor on the right. All the resistors are 47.3k

Bottom left of the IC goes to ground. I assume bottom right is VDD.

I believe the writing is N14D4 written both directions. Google gives nothing for various combinations.

PCB section and subject IC

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  • \$\begingroup\$ Perhaps it is some form of TVS or transient voltage suppressor. It could also be a level translator. I'd try scoping the MCU pin and feed in an analog voltage of -12v to +12v (with some sane series resistance, such as 4.7k) on the serial bus line to see what reached the MCU. From this it can likely be determined what kind of part it is. Maybe temporarily cut the serial line for this test, then bridge it after. \$\endgroup\$ – rdtsc Aug 11 at 14:02
  • \$\begingroup\$ I am probably completely out to lunch here, but I would investigate the possibility that the chip is one of the "Tiny Gate" devices that were extremely popular several years ago. That's what comes to mind when I look at the part number. \$\endgroup\$ – Dwayne Reid Aug 11 at 17:23
  • \$\begingroup\$ Marking is antisymmetric, so you can place the part either way. That would imply that it's some kind of diode array or a pair of MOSFETs (2x PMOS or 2x NMOS). \$\endgroup\$ – desqa Aug 12 at 9:42
  • \$\begingroup\$ diodes.com/assets/Datasheets/ds30345.pdf \$\endgroup\$ – Sean.Mollet Aug 12 at 15:55
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Desqa's comment, combined with rdtsc was enough to figure it out. It is functioning as a level shift.

It IS reversible and it's a pair of NPN transistors. I figured it was a SOT6 package, googling n14 sot6 led me to here:

https://cdn.instructables.com/ORIG/FH3/DM1V/HRTWJLSB/FH3DM1VHRTWJLSB.pdf

From there, I found DDC114YU, which led me to

https://www.diodes.com/assets/Datasheets/ds30345.pdf

That's exactly what it is, the GPIO is triggering the left transistor for transmit mode, and the resistor at the top drives the right transistor when in receive mode.

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    \$\begingroup\$ Sweet, I'm glad you found it out! My bad for assuming it's mosfet. \$\endgroup\$ – desqa Aug 12 at 16:29
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    \$\begingroup\$ The reversible thing was the real key. Nice job thinking of that \$\endgroup\$ – Sean.Mollet Aug 12 at 20:41

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