PropStick and Professional Development Board
Looking at the PropStick pictures makes it look like the DB9 port needs to hang down the side of the breadboard and that it might be a problem with the PDB. Would it be possible to leave the DB9 off the PropStick and use the PDB's RS-232 port instead? (The one next to the RJ-11 jack, not the BS2 programming port.)
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OS-X: because making Unix user-friendly was easier than debugging Windows
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OS-X: because making Unix user-friendly was easier than debugging Windows
Comments
A better option with less risk of straining the pads would be to solder jumper wires to them and a separate set of jumper wires to the DB9; then use the breadboard to connect the ends.
I can't speak to any other issues surrounding the PDB, since I've never used it. But do watch your voltage levels. The Propeller pins don't like anything above 3.3V without some kind of protection.
-Phil
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OS-X: because making Unix user-friendly was easier than debugging Windows
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OS-X: because making Unix user-friendly was easier than debugging Windows
http://forums.parallax.com/showthread.php?p=577939
-Phil
Post Edited (Phil Pilgrim (PhiPi)) : 5/5/2006 3:00:18 AM GMT
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OS-X: because making Unix user-friendly was easier than debugging Windows
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1+1=10
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OS-X: because making Unix user-friendly was easier than debugging Windows
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Jon Williams
Applications Engineer, Parallax
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OS-X: because making Unix user-friendly was easier than debugging Windows
Here is data I took on the characteristics of the positive side substrate diode. I didn't test the (-) side diode, but from what Chip said I would expect it to be very similar. The diode starts passing current at 0.4 volts above the 3.3 volt supply, and shows the expected exponential behavior.
In order to keep the current through the substrate diode near 100 microamps with a 5 volts input, you have to use a 10kohm series resistor, and for anything low speed (<1mhz) at the pin, I would opt for that.
With 1kohms the diode has to pass about 1.1 milliamps, which is not bad either for higher speed, up to 10mhz or so.
With 100 ohms the diode would have to pass about 10 milliamps. I pushed it to over 13 milliamps without any evident damage, but I wouldn't push my luck to far! For this kind of speed, a better level translator from 5 to 3.3 volts would be a better option.
It would be wise to include a zener diode or some such clamp to absorb parasitc current, so that it doesn't get into the substrate diode in the first place.
Another consideration is parasitic power. The Propeller is capable of operating at micro power, microamps at 20khz. Most voltage regulators are not capable of sinking current, so it is possible for parasitic power to come into the circuit through a substrate diode and supply power to the Propeller, and even push the power supply voltage up to a level greater than 3.3 volts. You would have to be especially careful about this when using something like a 12 volt input from something like RS232. The Propeller might handle 5 volts, but 12 volts would be a stretch. (disclaimer: I haven't tested that!)
The thread also contained discussion on frequency breakpoints vs the input resistance.
Tracy Allen
www.emesystems.com
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Tracy Allen
www.emesystems.com
Post Edited (Tracy Allen) : 5/5/2006 6:11:14 AM GMT
-P.
I too, will have the need to deal with this, so I ask. We may want to dedicate a post to this...
-Parsko
Why not take a 40pin IC-socket(or two) and place them on the PDB first, then the PropStick on top of hem, to raise it up and create the necessary clearance?
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Don't visit my new website...
In the PropSTICK schematic the Propeller's A31 is connected to the MAX3232's R2OUT, A30 is connected to T2IN, RSTn is connected through a transistor to R1OUT, and the MAX3232's T1IN is grounded. I want to use the PDB's RS-232 port. It has RTS, TX, CTS, and RX. How do those correspond to R2OUT, T2IN, R1OUT, and T1IN?
Also, in Jon's photo, it doesn't look like the Propeller's Vdd on pin 32 is connected. Is that correct?
On the 24LC256, the PropSTICK has 4.7k resistors between Vdd/SDA and Vdd/SCL. In Jon's photo it looks like he doesn't have a resistor between Vdd and SCL.
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OS-X: because making Unix user-friendly was easier than debugging Windows
It might be the internal pullups alone in the Propeller is faster. It might be economy as the resistors are getting tiny and each one might be a bit of a hassle in production.
The Propeller Demo board shows only the SDA line with a 10K pullup but it is linked to the RESn line.
The Homebrew Board discussion of Mike Cook's talks about the Pro and Con.
It is·here and it will explain a lot.
http://forums.parallax.com/showthread.php?p=579595
I would use both on the PropSTICK until I found a reason not to. You may want to add other chips to the I2C line and need them as the bus gets stacked.
When the day comes that you find a need to remove the SCL pullup [noparse][[/noparse]likely never], it would take very little to bypass it with a bit of wire and a dab of solder.
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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
Post Edited (Kramer) : 5/12/2006 6:01:46 PM GMT
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OS-X: because making Unix user-friendly was easier than debugging Windows
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OS-X: because making Unix user-friendly was easier than debugging Windows
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OS-X: because making Unix user-friendly was easier than debugging Windows
Thanks for sharing your experience! I've been somewhat at a loss advising people about whether the 'Stick will work with the PDB, since I don't have a PDB myself. Your photo says it all!
Cheers!
Phil