Help a newb / Why can my sx fry my eggs?
wikst
Posts: 4
Hello,
this is my first post here and it also concernes my first attempt to program a sx. The problem is that my sx got fried as I connected it for programming (followed Practical SXB and connected it as in sxkeyman2_0 page 13).
After my chip had gotten fried I started testing what could be wrong, and found that both on my fried chip and on a fresh one, if i connected·5V -> 470 Ohm -> led -> Vdd-pin, Vss-pin -> gnd the led was on.
So the question is: What have I missed?! I can't see that the vdd-pin and the vss-pin are supposed to be internally connected =P
The chip I have is a 28-pin sx with the text "sx28AC/DP-G 0602", (and the programming device I have is a blitz).
Regards
/Esa
·
this is my first post here and it also concernes my first attempt to program a sx. The problem is that my sx got fried as I connected it for programming (followed Practical SXB and connected it as in sxkeyman2_0 page 13).
After my chip had gotten fried I started testing what could be wrong, and found that both on my fried chip and on a fresh one, if i connected·5V -> 470 Ohm -> led -> Vdd-pin, Vss-pin -> gnd the led was on.
So the question is: What have I missed?! I can't see that the vdd-pin and the vss-pin are supposed to be internally connected =P
The chip I have is a 28-pin sx with the text "sx28AC/DP-G 0602", (and the programming device I have is a blitz).
Regards
/Esa
·
Comments
The SX is going to use some amount of power, that power is going to make the LED light up.
What is the voltage measurement between the Vdd and Vss pins when you do this experiment ? If it's zero volts, then there is a problem (short).
Bean.
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Uhhhm, that was on fire when I got here...
www.iElectronicDesigns.com
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The voltage between Vdd and Vss is 2.85V with my test settup, wich means that the resistence between Vdd and Vss is about 1kOhm if you use some current laws, but when I measure the resistance between the pins without having the chip connected to anything, it shows between 0.6MOhm and 1.6MOhm, and when I connected my first (now fried) chip it melted the plastisc on my experiment before I realised what was happening.
So it seems to me that the internal resistance decreases with increased voltage/current?
Since both the chips I've tried with had simular responce, either both the chips came from a faild series, or more likely: The settup is for some reason wrong.
Is it therefor possible that the misstake is in some of the following:
* Old version of chip -> different pin assignment from sxkeyman2_0
* Misred pin assigment (assumed chip was looked at from above for example)
* Mistake regarding persumption of modell (I have 28 long pins..
* Lack of knowledge: do I need any futher comonents or pins assigned to make the internal resistance between Vdd and Vss high and stable to avoid short circuiting the chip?
* The uC gods are just testing my spirit
?
Thanks for the responce Bean, let me know if this told you something.
Esa
Post Edited (wikst) : 6/26/2008 2:48:24 PM GMT
Make sure your 5V is REALLY 5V and not much higher (5.5V is the max the chip can take).
Does the chip get really hot ONLY after you try to program it ?
Are you using one of the SX protoboards ? Or just a regular breadboard ?
Do you have /MCLR connected to a 10K to Vdd ?
Do you have a cap between Vss and Vdd close to the SX ?
In my experience, as all you need to program it is Vss to ground, Vdd to +5, MCLR to a 10K to Vdd, a bypass cap between Vss and Vdd, And OSC1 and OSC2 connected to the programmer.
Does the chip say Scenix, Ubicom, or Parallax on it ?
Bean.
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Uhhhm, that was on fire when I got here...
www.iElectronicDesigns.com
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How big cap is suitable?
Bean.
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Uhhhm, that was on fire when I got here...
www.iElectronicDesigns.com
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Thx a lot Bean!
/esa