Re: [avr-gcc-list] ok, so this message *is* off-topic

[Brian Dean]

On Tue, Nov 16, 2004 at 03:02:19PM -0800, address@hidden wrote:

> I'm a programmer who's getting his feet wet with microcontroller
> hardware and programming.  I don't understand all this stuff about
> jtag, ice, isp, etc.  When I see remarks on the Atmel page about how a
> "programmer isn't needed" my reaction is "I'm not needed?" but
> obviously they're talking about something else.

All AVR's, at some point, need a programmer to download the compiled
binary instructions into their flash memory - this is the program they
run.  The most common method of doing that is ISP - In System
Programming, which uses a simple SPI style interface (SPI is an
industry standard synchronous serial interface method).  Typical
programmers using this method are Atmel's AVRISP and STK500 devices
($30 and $80 respectively).  JTAG is another method of programming, it
also has a second advantage in that one can use it for debugging as
well, i.e., single-step debugging through your program, examine
variables, set breakpoints, etc.  Typical programmers for this method
are Atmel's JTAGICE programmer and third party boards like Graham's
($300 and $40 respectively).  Not all AVRs support JTAG, usually only
those with 40 pins or greater, and even not all those, I'm sure there
are exceptions.

Boards that say "no programmer needed" are typically pre-programmed
with a bootloader program.  Many newer ATmega AVRs support a
bootloader feature such that they can "self-program", i.e., when they
come out of reset they can then load a new program through a serial
port or other interface and reprogram themselves.  In this case, you
at least need a way to transfer the program into the AVR such as a PC
with a serial port, but you don't need a seperate AVRISP, STK500, nor
JTAGICE type programmer.  The Butterfly fits in this category - it's
got a bootloader built-in.

Hope this helps ...

-Brian
-- 
Brian Dean
BDMICRO - ATmega128 Based MAVRIC Controllers
http://www.bdmicro.com/