search

screamingbubble / mega-isp

Automatically exported from code.google.com/p/mega-isp
0 stars 0 forks source link

SCK low ---before--- RESET #22

Open GoogleCodeExporter opened 8 years ago

GoogleCodeExporter commented 8 years ago 
The AVR ISP documentation...
http://www.atmel.com/dyn/resources/prod_documents/doc0943.pdf

...states that... "SCK ... Immediately after the Reset goes active, this pin 
will be driven to zero by the programmer."

The opposite is performed in start_pmode...

  // RESET ---not--- active
  pinMode(RESET, OUTPUT);
  digitalWrite(RESET, HIGH);

  // SCK driven low
  pinMode(SCK, OUTPUT);
  digitalWrite(SCK, LOW);

  delay(50);

  // RESET active
  digitalWrite(RESET, LOW);

  delay(50);

If the target is driving SCK high when start_pmode is entered, this code 
creates a short-circuit for 50 ms.  More than enough time to damage both 
processors.

http://code.google.com/p/mega-isp/source/browse/trunk/avrisp/ArduinoISP.pde#241

Original issue reported on code.google.com by arduino....@gmail.com on 15 Jun 2011 at 4:45

GoogleCodeExporter commented 8 years ago

Original comment by rsb...@gmail.com on 25 Jun 2011 at 3:02