DTR reset pulse
Dr_Acula
Posts: 5,484
Pullmoll and several others have been trying to get the reset pulse to work reliably with BST. The circuit works fine with the propeller tool and it works on some hardware configurations and not others.
There are several scenarios with the reset depending on the circuit
1) The reset happens the entire time DTR is high and is only released out of reset when it goes low
2) Reset happens on the negative to positive transition
3) Reset happens on the positive to negative transition
Problems have arisen using option 2), in particular with a NPN signal transistor and a high pass filter with a 0.01uF and a 10k resistor. This will produce a positive going pulse on the positive edge transition and hence reset the propeller at the beginning of the reset pulse.
Option 1) would be valid if the DTR pulse went through a max3232 and then into the propeller.
Juergen (pullmoll) has replaced the NPN (BC549 or any small signal NPN) with a PNP transistor (BC558 but any will work eg 2Nseries) and this circuit is option 3) and resets on the negative transition, where the base is briefly pulled under 3.3V. See attached schematic.
The transistor download circuit is based on this one www.parallax.com/dl/docs/prod/prop/PropDemoDschem.pdf
The series 10k may not be needed on the circuit below.
I am not sure why this is not an issue with the propeller tool but possibly the reset pulse is of a shorter duration.
Comments and thoughts would be most appreciated.
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www.smarthome.viviti.com/propeller
Post Edited (Dr_Acula) : 3/24/2010 9:22:05 AM GMT
There are several scenarios with the reset depending on the circuit
1) The reset happens the entire time DTR is high and is only released out of reset when it goes low
2) Reset happens on the negative to positive transition
3) Reset happens on the positive to negative transition
Problems have arisen using option 2), in particular with a NPN signal transistor and a high pass filter with a 0.01uF and a 10k resistor. This will produce a positive going pulse on the positive edge transition and hence reset the propeller at the beginning of the reset pulse.
Option 1) would be valid if the DTR pulse went through a max3232 and then into the propeller.
Juergen (pullmoll) has replaced the NPN (BC549 or any small signal NPN) with a PNP transistor (BC558 but any will work eg 2Nseries) and this circuit is option 3) and resets on the negative transition, where the base is briefly pulled under 3.3V. See attached schematic.
The transistor download circuit is based on this one www.parallax.com/dl/docs/prod/prop/PropDemoDschem.pdf
The series 10k may not be needed on the circuit below.
I am not sure why this is not an issue with the propeller tool but possibly the reset pulse is of a shorter duration.
Comments and thoughts would be most appreciated.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
www.smarthome.viviti.com/propeller
Post Edited (Dr_Acula) : 3/24/2010 9:22:05 AM GMT
850 x 560 - 41K
Comments
I don't know either. The showstopper before the modification was that the DracBlade would reset while DTR was high and any character was sent over TX. Don't ask me why, it just happened to be so. Now since most terminal software defaults to setting DTR high while a connection is open, I could not use it. I modified gtkterm, which I use, to take the DTR low immediately, but also this short pulse caused a reset (of course). The other downside was I could not load a program to RAM only and then start the terminal, because the reset wiped it out.
Now I'm happy with how it is and can use either BST or BSTC as it ought to be.
Juergen
PS: Note that you have to bend an PNP transistor's middle pin backwards to meet the PCB's holes. The flat side of the transistor (if it has one, that is) is towards the boards edge.
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He died at the console of hunger and thirst.
Next day he was buried. Face down, nine edge first.
Post Edited (pullmoll) : 3/24/2010 9:20:08 AM GMT
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You only ever need two tools in life. If it moves and it shouldn't use Duct Tape. If it does not move and it should use WD40.
be sure that the propeller reset signal is generated at the end of the DTR signal.
On my last board the propeller reset was generated on the start of the DTR signal and the bootload was very
flaky. I had inverted the DTR signal twice by mistake causing all the problem's.
Russ