Reset Circuit on the PropPlug - Why do we need it???
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Firstly, let me explain why the reset circuit is used...
The DTR pin is used to reset the prop. DTR is a negative active at TTL level (i.e. 0V = DTR ON, 3V3 = DTR OFF). When the DTR pin is steady state (either on or off), the transistor circuit is turned off, and no reset takes place. When the DTR pin is turned off, the DTR (TTL) pin goes high and this charges the series capacitor. The transistor turns on until the cap is discharged by the ground 10K resistor, creating a ground pulse on the Reset pin of the prop.
It seems to me that an inverter from the DTR output pin of the FT232R chip would serve just as well, although some timing change may be necessary in the software, since currently the reset pulse is being timed from the start of DTR going OFF, rather than timed from DTR going on. Anyone done any timing here???
Now, how could we avoid this circuit totally???
If we changed the software, such as the PropTool (as an option), or bst (as an option), or Propellant or indeed any other download software, we could indeed avoid this additional hardware (transistor circuit or an inverter). How???
Well, if we the software download code had an option to invert the use of the DTR pin, this should work (maybe a timing change required, but it should work from what I can see). So, the software would pulse/set DTR ON, then a small delay, and set DTR OFF. The prop would be reset when DTR was ON. Once DTR goes OFF the propeller would startup. So, the download software would be required to keep DTR OFF. This means that the software would be required to remain active and DTR held OFF.
However, this method would allow lots of other standard plugs to work. It would happily program the prop's eeprom simply. Then the user could remove a reset (DTR) link and continue working.
This is certainly not an elegant solution, but it gives a programming option without having to build the reset circuit.
Perhaps an alternative would be to just have a simple download program that would achieve this from an already compiled program.
Any thoughts or comments???
The DTR pin is used to reset the prop. DTR is a negative active at TTL level (i.e. 0V = DTR ON, 3V3 = DTR OFF). When the DTR pin is steady state (either on or off), the transistor circuit is turned off, and no reset takes place. When the DTR pin is turned off, the DTR (TTL) pin goes high and this charges the series capacitor. The transistor turns on until the cap is discharged by the ground 10K resistor, creating a ground pulse on the Reset pin of the prop.
It seems to me that an inverter from the DTR output pin of the FT232R chip would serve just as well, although some timing change may be necessary in the software, since currently the reset pulse is being timed from the start of DTR going OFF, rather than timed from DTR going on. Anyone done any timing here???
Now, how could we avoid this circuit totally???
If we changed the software, such as the PropTool (as an option), or bst (as an option), or Propellant or indeed any other download software, we could indeed avoid this additional hardware (transistor circuit or an inverter). How???
Well, if we the software download code had an option to invert the use of the DTR pin, this should work (maybe a timing change required, but it should work from what I can see). So, the software would pulse/set DTR ON, then a small delay, and set DTR OFF. The prop would be reset when DTR was ON. Once DTR goes OFF the propeller would startup. So, the download software would be required to keep DTR OFF. This means that the software would be required to remain active and DTR held OFF.
However, this method would allow lots of other standard plugs to work. It would happily program the prop's eeprom simply. Then the user could remove a reset (DTR) link and continue working.
This is certainly not an elegant solution, but it gives a programming option without having to build the reset circuit.
Perhaps an alternative would be to just have a simple download program that would achieve this from an already compiled program.
Any thoughts or comments???
Comments
So no inverter needed. Just a 10nF capacitor between /DTR out and RESn input (BOE must be Low).
I use such a circuit since years to program my Propellers.
Andy
Andy
My objective is to remove the requirement for the extra components.
Another option could be to use one of the CBUSn pins? (postedit: RI is an input to FT chip)
Andy: Perhaps I should look at the FT-Prog tool to see what could be done.
Postedit:
OK looked at the FT-Prog tool and the lines can be inverted, so we could use this and give a short pulse to the DTR line. I didn't find anything about configuring the CBUSn pins.