> From:         Olin Lathrop[SMTP:olin_piclist@EMBEDINC.COM]
> Sent:         Sunday, February 08, 2004 8:24 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: [PIC]: PIC programmer puzzle

>> 4) Signal line ringing issues due to improper line termination?
>> Perhaps 270 ohm series resistors instead of 2000 ohm resistors?

> I don't want to go much below 2Kohm for other reasons, but you're getting
> close.

Line termination must be done at both ends of the line. Your line has 2k
resistors at the source end (the controller PIC); it also needs termination
at the load end. Voltage overshoot can occur at the open end of the line.
Putting the target PIC in the ZIF socket exposes it only to the input of the
line. Put it at the other (open or misterminated) end exposes it to transients
which are not seen at the source. You have resistors to ground on the Vdd
and Vpp lines, but you said nothing about the clock and data lines.

Capacitors to ground from the end of the 2k resistors would calm things
down. Terminating resistors at the breadboard end would be better if the
controller could drive them (but not with series 2k resistors).

John Power

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