PGD PGC Crosstalk

[3v0]

This is from your earlier post. and Bill has indicated that he followed Micrchip order. and it is

VPP, VDD, GND, PGD,PGC, (aux)(PICKIT2 version.)

so I felt the order is suggested to be changed for a new designer. Yes I do agree that it serves reduce the crosstalk. but then on that programmer doesn't become compatible to meant ready boards using Microchip version. This is what I tried to indicate, please.

This is what I am doing. As I said it does not change the order of the signals at the connectors. Only at the cables.

At the first IDC the order is
VPP, VDD, GND. PGC, PGD

after the wires leave the connector they become
PGD VDD GND PGC VPP

Just prior to the other connector they move back to
VPP, VDD, GND. PGC, PGD

OR

9 10 3 4 5 6 7 8 1 2
1 2 3 4 5 6 7 8 9 10
...
1 2 3 4 5 6 7 8 9 10
9 10 3 4 5 6 7 8 1 2

I make a slit between the 2 and 3 wire and the 8 and 9 wire
The 1 2 wires are moved to where the 9 10 wires were and
the 9 10 take the place of the 1 2 wires. This is done on both ends.

The process of moving wires in this way has been used in PC floppy drive cables for years. Nothing strange.

Look at the picture, neither the Junebug or the target has been changed to take the new cable. Better yet it is WORKING with a 35 inch cable

 

[petrv]

Hi 3v0,

this long ICSP cable actually works ? wow ...

Petr

 

[mvs sarma]

This is what I am doing. As I said it does not change the order of the signals at the connectors. Only at the cables.

At the first IDC the order is
VPP, VDD, GND. PGC, PGD

after the wires leave the connector they become
PGD VDD GND PGC VPP

Just prior to the other connector they move back to
VPP, VDD, GND. PGC, PGD

OR

9 10 3 4 5 6 7 8 1 2
1 2 3 4 5 6 7 8 9 10
...
1 2 3 4 5 6 7 8 9 10
9 10 3 4 5 6 7 8 1 2

I make a slit between the 2 and 3 wire and the 8 and 9 wire
The 1 2 wires are moved to where the 9 10 wires were and
the 9 10 take the place of the 1 2 wires. This is done on both ends.

The process of moving wires in this way has been used in PC floppy drive cables for years. Nothing strange.

Look at the picture, neither the Junebug or the target has been changed to take the new cable. Better yet it is WORKING with a 35 inch cable

Now I got your point, 3v0. thanks for the elaboration.

 

[3v0]

Sarma,
Not a problem.

Hi 3v0,

this long ICSP cable actually works ? wow ...

Petr

Let me say that it seems to work. I have run about 50 download verifies without a problem. That is not a lot, and without a control (unmodified cable of same length) there in nothing to compare it to.

You/anyone is welcome to build one and give it a try.

 

[mvs sarma]

Dear 3v0, I just happened to see a note in DL4YHF site . I am attaching the extract under quote and the link details for general interest on cross talk issue. Perhaps it can be useful.
"
(*) About PGD and PGC filtering: There was a note on the Microchip forum (by Olin Lathrop) about programming the dsPIC30F201(**), suggesting to put 22..47 pF on the PGD and PGC lines to ground near the target chip. In addition, put a 100 ohm resistor in series with the PGD line between target chip and the cap. The resistor and cap on the PGD line low pass filter the PGD signal when it is driven by the target chip. This reduces the high frequencies that can couple onto the PGC line. The cap on the PGC line makes it less suceptible to coupled noise.
(**) We later found out that this important note also applies to the PIC18Fxxxx family. A user of a Velleman PIC programmer reported success with a PIC18F4520 after adding 2 * 33 pF caps and a 100 Ohm series resistor.

https://www.qsl.net/dl4yhf/winpic/index.htm#pgd_pgc_filtering "

 

[3v0]

Good find.

As the speed between the programmer and target increase the problems will get worse. But at this point not everyone agrees that there is a problem.

Thanks

 

[e_1069]

current limit

I have never had an issue with crosstalk and the ICD. I don't have a problem with the order of the pins. However there may be issues with wire gauges and spacings. Also supply capacitance. If I were experiencing crosstalk I would make sure my supply was clean during a program.

Also I might try and put a small resistor in series with PGC and PGD to lower the currents. Something like 1-5 maybe even 10 Ohms shouldn't affect the outputs but still reduce the radiated energy from the wires by limiting the current.

OK. so like a dumba$$ I didn't read the whole thread before posting but still. Though I might help, but it looks like you have it.