AVR-Chat

Ryan wrote:

> I'm going to take the step away from DIP, to TQFP!  WOOO!!!  My next
> design is going to use the Mega16 in the 44pin TQFP package. 
> Obviously I can't use my STK500 to program it anymore.

Why is that? You can run the ISP connections from the STK500 to your 
target board. This is documented in the STK500 manual.

> So - what do you use?

STK500
AVR-JTAG mkI clone by Olimex
AVR-JTAG mkII by Atmel
AVRISP mkI by Atmel

> 
> I've heard people mention a "JTAG"?  Does that allow complete
> programming?  Fuses and eeprom too?  Any special tips I need to know?

They support all the programming (see your datasheet for details, 
though). The JTAG units also allow debugging, typically.

> My second question, is how reliable is the internal RC clock?  It's
> tough for me to trust them, so I have been using an external
> crystal... but... in the interest of real estate, costs, and ease of
> assembly, I'm considering switching to the internal clock.  However -
> one thing I'm concerned about is the RS232 interface.  If the internal
> clock is 7.9mhz instead of the desired 8mhz, will that make a
> difference?  How are tolerances?

The RC oscillators can be trimmed to get them reasonably close. Refer to 
your datasheet for details (in the section called "calibrated internal 
RC oscillator").

You generally want the RS-232 to be within 2% or so (the tolerance is 
dependent on how the receiver samples the signal).

There are details on calibration schemes in the datasheet as well as:
http://atmel.com/dyn/resources/prod_documents/doc2555.pdf
http://atmel.com/dyn/resources/prod_documents/doc2563.pdf
http://atmel.com/dyn/resources/prod_documents/doc8002.pdf

-- 
Ned Konz
ned@bike-nomad.com
http://bike-nomad.com