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I was exploring one of the popular Tiva C launchpad (http://processors.wiki.ti.com/index.php/Tiva_C_Series_LaunchPads) to create a custom board based on TM4C123GXL evaluation kit.

There is a Schottky diode connected to the RESET output of the voltage supervisor in the schematic as shown below

enter image description here

One of the anodes goes to the RESET pin of the main microcontroller and the other one to the RESET pin of another microcontroller which act as an inbuilt debugger/programmer.

What is the use of a Schottky diode in the output of a voltage supervisor like this?

Note : +VBUS is the +5V coming from USB connector

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  • \$\begingroup\$ The diodes are placed so –TARGETRST and –ICDI_RST can't influence each other. \$\endgroup\$ – Janka Nov 20 '18 at 4:24
  • \$\begingroup\$ It's sometimes called a "diode-or." However, the polarity of the diodes looks a little odd to me. \$\endgroup\$ – jonk Nov 20 '18 at 4:45
  • \$\begingroup\$ I have just had to deal with an ST microcontroller that holds its own RST pin low during start-up. We have to do something similar to protect other devices on the shared RST line from being affected \$\endgroup\$ – The Photon Nov 20 '18 at 5:12
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The voltage supervisor can pull both TARGETRST and ICDI_RST low but TARGETRST cannot pull ICDI_RST low or vice versa.

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It's a little confusing (the diodes look backwards) because you can't see where the other lines go- to two RC circuits with pullups.

enter image description here

enter image description here

The supervisor chip pulls both resets (active) low, but the RESET pushbutton does not affect ICDI_RST.

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  • \$\begingroup\$ According to the polarity of the Schottky diode shown in the pic, the 10K pull-up resistor on voltage supervisor output seems useless. Please correct me if I am wrong. \$\endgroup\$ – Supreeth Nov 20 '18 at 5:36
  • \$\begingroup\$ I think you're basically right, with 10K resistors even at high Ta leakage isn't all that significant. \$\endgroup\$ – Spehro Pefhany Nov 20 '18 at 5:44

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