PGD PGC Crosstalk - Electronic Circuits Projects Diagrams Free

3v0 · 13th April 2008, 12:07 AM

The first time I seen the ICSP cables with PGC and PGD adjacent to each other I suspected it was not a good idea. As the technology is applied to ever faster chips crosstalk has got to be a limiting factor.

If anyone is designing a PIC programmer I suggest changing

VPP, VDD, GND. PGC, PGD
to
VPP, PGC, GND, VDD, PGD

This should eliminate crosstalk.

There is a short discussion on the subject at
http://www.embedinc.com/picprg/icsp.htm
Under the section header PGC to PGD Crosstalk.

You can toss rotten fruit at me if you like...

mister_e · 13th April 2008, 12:19 AM

To me
VPP, Vdd, PGC, Gnd, PGD

Could be a better option, keeping programming pins away of "higher voltage" signals.

3v0 · 13th April 2008, 12:28 AM

Quote:

Originally Posted by mister_e

To me
VPP, Vdd, PGC, Gnd, PGD

Could be a better option, keeping programming pins away of "higher voltage" signals.

Could be. Here was the logic I used.
I know a 5 pin ICSP can be inserted backward with a ICD2 or PICkit2 without damag. Switching VDD and PGC preserves this.

Reversing your cable will switch VDD and GND and I think that would be a problem.

blueroomelectronics · 13th April 2008, 01:14 AM

The reason most use VPP,+5,GND,PGD,PGC is it's the order Microchip uses on their programmers. Short cables keep the problem to a minimum.

Microchips Real ICE suggests a differential cable at clocks above 40MHz.

donniedj · 13th April 2008, 01:57 AM

The rate of flash memory burning is the only true problem. When flash burn is not the bottle neck, the very programming device is capable of pushing a clock above 40MHZ is not the bottle neck, then I will be concerned.

Since a 60 inch cable has not ever caused a programming failure, any talk of crosstalk is snake oil in my ears. Off to the bath house I go.

blueroomelectronics · 13th April 2008, 02:02 AM

What programmer are you using?

3v0 · 13th April 2008, 02:03 AM

Quote:

Originally Posted by blueroomelectronics

The reason most use VPP,+5,GND,PGD,PGC is it's the order Microchip uses on their programmers. Short cables keep the problem to a minimum.

Microchips Real ICE suggests a differential cable at clocks above 40MHz.

I understand your reason. With the addition of a simple adapter your programmer is compatible with Microchip. What I do not understand is Microchips reason. These things are getting faster and it is starting to bite them. It would have been easy to do better.

At would be nice to use a longer ICSP cable. It could possibly fix that occasional programming error.

Like I said. Feel free to throw fruit. I know I am going against the grain.

blueroomelectronics · 13th April 2008, 02:11 AM

When I designed the Inchworm I sweated over the pinout and connector.

3v0 · 13th April 2008, 02:48 AM

One could quite possibly get the same benefit by using a cable that switched the signals at each end. With some care one could cut the 3-4 and 7-8 pairs loose and swap them at the IDC connectors. I will make up an 18 inch cable and give it a try. If it works it is the best of both worlds.

Quote:

Originally Posted by blueroomelectronics

When I designed the Inchworm I sweated over the pinout and connector.

Both the inchworm an Junebug are great programmers. I like the 2x5 connectors a lot. They have redundant circuits and are dead easy to make. The choice is/was a good one. In terms of sales compatibility is a big issue. I understand that.

Still I think Microchips decision to put PGC and PGC next to each other is a poor one. IFF switching the two signals allows the use of longer cables and more reliability that would be a good thing. The down side is that to connect to other peoples targets you would have to use an adaptor with crossed wires.

3v0 · 13th April 2008, 04:32 AM

I have built a 35 inch twisted ICSP cable. It seems to be working.

The construction is easier then I first indicated. All you do is cut the outside two wires loose and move each pair to the other side of the cable. Both ends. Rip the wires down far enough such that you can lay them flat under the strain relief.

I know a few downloads and verifies are not enough to declare success. I will let you know in a week if it works well or sooner if not. The other thing that needs to be pointed out is that I did not make a 35 inch standard cable to compare it against. Given that the Microchp instructions suggest a cable under 6 inches that does not sound like a good idea. Try it if you like.

The picture is large to show the cable ends.

conductors
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

Pommie · 13th April 2008, 05:27 AM

3v0,

Your image isn't showing and the IP address is 192.168.... which is a local address.

Mike.

3v0 · 13th April 2008, 05:43 AM

Quote:

Originally Posted by Pommie

3v0,

Your image isn't showing and the IP address is 192.168.... which is a local address.

Mike.

Dag Nabit Anyway

Fixed it.

mvs sarma · 13th April 2008, 06:57 AM

Though difficult, let us try shielded wire for either PGC or PGD (one of them would do)wires with shield grounded at one end. this would help I feel.

blueroomelectronics · 13th April 2008, 03:43 PM

I recall seeing sheilded ribbon cable, and twisted pair ribbon cable (not sure twisted pair would make any difference on this though)

mvs sarma · 13th April 2008, 04:48 PM

we cant go on changing the standards while we can shield one wire by a bypass cable and still maintain the order. screened interconnect cable patches are not uncommon in RF circuitry, i remember. entire ribbon is embedded in shield. it wont help. At times a 22E resistor in series to clock wire and a 22-47pf cap to ground close to load side,reduces the crosstalk

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13th April 2008, 12:07 AM	#1
3v0	PGD PGC Crosstalk The first time I seen the ICSP cables with PGC and PGD adjacent to each other I suspected it was not a good idea. As the technology is applied to ever faster chips crosstalk has got to be a limiting factor. If anyone is designing a PIC programmer I suggest changing VPP, VDD, GND. PGC, PGD to VPP, PGC, GND, VDD, PGD This should eliminate crosstalk. There is a short discussion on the subject at http://www.embedinc.com/picprg/icsp.htm Under the section header PGC to PGD Crosstalk. You can toss rotten fruit at me if you like... __________________ Please post questions to the forums. PM's are for personal communication. BCHS/3v0's Tutorials Junebug USB PIC programmer kit., USB Bit Whacker, The 15 Minute Printed Circuit Board! (+drill time)

13th April 2008, 12:19 AM	#2
mister_e	To me VPP, Vdd, PGC, Gnd, PGD Could be a better option, keeping programming pins away of "higher voltage" signals. __________________ Steve

13th April 2008, 01:14 AM	#4
blueroomelectronics	The reason most use VPP,+5,GND,PGD,PGC is it's the order Microchip uses on their programmers. Short cables keep the problem to a minimum. Microchips Real ICE suggests a differential cable at clocks above 40MHz. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com/

13th April 2008, 01:57 AM	#5
donniedj	The rate of flash memory burning is the only true problem. When flash burn is not the bottle neck, the very programming device is capable of pushing a clock above 40MHZ is not the bottle neck, then I will be concerned. Since a 60 inch cable has not ever caused a programming failure, any talk of crosstalk is snake oil in my ears. Off to the bath house I go.

13th April 2008, 02:02 AM	#6
blueroomelectronics	What programmer are you using? __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com/

13th April 2008, 02:11 AM	#8
blueroomelectronics	When I designed the Inchworm I sweated over the pinout and connector. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com/

13th April 2008, 04:32 AM	#10
3v0	35" ICSP cable works. large image alert I have built a 35 inch twisted ICSP cable. It seems to be working. The construction is easier then I first indicated. All you do is cut the outside two wires loose and move each pair to the other side of the cable. Both ends. Rip the wires down far enough such that you can lay them flat under the strain relief. I know a few downloads and verifies are not enough to declare success. I will let you know in a week if it works well or sooner if not. The other thing that needs to be pointed out is that I did not make a 35 inch standard cable to compare it against. Given that the Microchp instructions suggest a cable under 6 inches that does not sound like a good idea. Try it if you like. The picture is large to show the cable ends. conductors 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 __________________ Please post questions to the forums. PM's are for personal communication. BCHS/3v0's Tutorials Junebug USB PIC programmer kit., USB Bit Whacker, The 15 Minute Printed Circuit Board! (+drill time) Last edited by 3v0; 13th April 2008 at 05:41 AM.

13th April 2008, 05:27 AM	#11
Pommie	3v0, Your image isn't showing and the IP address is 192.168.... which is a local address. Mike.

13th April 2008, 06:57 AM	#13
mvs sarma	Though difficult, let us try shielded wire for either PGC or PGD (one of them would do)wires with shield grounded at one end. this would help I feel. __________________ Regards, Sarma.

13th April 2008, 03:43 PM	#14
blueroomelectronics	I recall seeing sheilded ribbon cable, and twisted pair ribbon cable (not sure twisted pair would make any difference on this though) __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com/

13th April 2008, 04:48 PM	#15
mvs sarma	we cant go on changing the standards while we can shield one wire by a bypass cable and still maintain the order. screened interconnect cable patches are not uncommon in RF circuitry, i remember. entire ribbon is embedded in shield. it wont help. At times a 22E resistor in series to clock wire and a 22-47pf cap to ground close to load side,reduces the crosstalk __________________ Regards, Sarma. Last edited by mvs sarma; 13th April 2008 at 04:51 PM.