Re: [avr-gcc-list] ponyprog interface explanation

[Ned Konz]

On Monday 10 January 2005 3:07 pm, jeffrey traer bernstein wrote:
> can anyone explain the ponyprog hardware interface to me? \
> http://www.lancos.com/siprogsch.html
> it's what i use but i really have no idea what's going on.
> I was under the impression one needed a little more than a few diodes to
> get between the +-12-15 V serial and ~5 V TTL levels.

The AVR isn't TTL; it's CMOS. There's very little TTL around any more. Anyway, 
R4-6 and Z1-Z3 limit the voltages at J2 to -0.6 .. +5.1 V for the sake of the 
CMOS. And D1-D3 keep the power supply cap (C3) charged from whichever of the 
pins 3,7/6, or 4 happen to be at a voltage > 6V (or 5V + dropout of 
LM2963Z-5, whatever that is).

> and what's the deal with the transistor for the reset?

Assuming that the reset line is pulled up by a resistor, it converts the 
relatively low-current RS-232 signal into a strong pull-down for the reset 
line.

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