In SX Microcontrollers, SX/B Compiler and SX-Key Tool, dkemppai wrote:

[quote="Guenther Daubach"]
Dan,

several users (including me) had trouble with "Chip connection failed" errors when the SX (or better the SX-Key) was not powered close to 5 Volts. I came across this problem fairly often when using an SX-Tech board with just a 1µF cap attached to the regulator's output pin. Since I'm using a 22µF cap instead (as the LM 2940 datasheet recommends), these problems are gone. Looks as if the SX-Key generates a spike on Vdd when the programming voltage is turned on that can cause trouble when not filtered out sufficiently.

[/quote]Guenther,
 

The 2940 is an LDO. Som LDO's are very picky about filter caps (Value and ESR). I've seen order of magnitude changes (.1uF instead of 1uF) send them into oscillations! Looking at my SXtech board, there is only a 1uF cap on that one also (I've never really looked closely at the board!). It also appears that there is about an inch of copper from the cap to the regulator (adding to ESR/ESL). Not only that, but there is a "T" in the trace with the cap on the opposite leg as the MCU and the SX-Key...   ...maybe some notes to add for the next revision of the Tech board.    

 

Anyway, As per your suggestion, I looked at the 5 volt signal. No problems there. The voltage drops about 75mV for 5uS worst case. The amplitude is less than the clock noise on the VCC line with the SX key is supplying the clock.

 

But, its working now. So, I'll keep programming until it quits. It's got to be a connection somewhere! 

 

-Dan

---------- End of Message ----------


You can view the post on-line at:
http://forums.parallax.com/forums/default.aspx?f=7&p=1&m=82811#m83011

Need assistance? Send an email to the Forum Administrator at forumadmin@parallax.com

The Parallax Forums are powered by dotNetBB Forums, copyright 2002-2005 (http://www.dotNetBB.com)