Why the high-pass filter on DTR of the Prop-Clip & Co?

Remy Blank

While looking at the schematics of the demo board, I was wondering why there was a high-pass filter on the DTR -> RESn? My understanding is that this will generate a short fixed-length pulse on RESn on the rising edge of DTR, and will not allow keeping the Propeller in reset through the serial interface. Why not just connect DTR to the transistor (through a 10k resistor)?

-- Remy

Gadgetman

Because that's the way the Propeller boot process works?

After a Reset it will wait for a certain period to receive communication on the serial port.
Then, if that is unsuccessful, it will attempt to load an image from an EEPROM.

No need to hold the Reset line.

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Remy Blank

I understand there's no *need* to hold the reset line. But I have an application where I *want* to hold the reset line, and I just wanted to know if there was a specific reason for having that capacitor.

When programming the Propeller, DTR is set, and reset a few milliseconds afterwards. So there's no real need for the filter. Unless I'm missing something.

Gadgetman

My guess is that it's because some USB-RS232 adapters play fast and loose with the standards, and so does some Terminal programs.
(In other words, they may keep the DTR at an 'undesired' state, keeping your Propeller in a state of Reset... )

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