PGD PGC Crosstalk - Page 2 - Electronic Circuits Projects Diagrams Free

3v0 · 13th April 2008, 04:58 PM

The cable mod I have SEEMS to be working. I am thinking that if it does not the chance of the shielded cable working is small. Reason is that Microchip claims the problem is reflections rather then cross talk. That can be fixed too but not as easily.

3v0 · 13th April 2008, 05:01 PM

Quote:

Originally Posted by 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

What are you taking about?
My cable mod uses the same pinout as Bill uses on his programmers and is easy to construct.

mvs sarma · 13th April 2008, 05:10 PM

Quote:

Originally Posted by 3v0

T.............
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.

............

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.

blueroomelectronics · 13th April 2008, 05:11 PM

Well the programmer has a pair of 4.7K pulldowns, would another pair of 4.7K on the target balance the cable and reduce reflections?

mvs sarma · 13th April 2008, 05:14 PM

Quote:

Originally Posted by blueroomelectronics

Well the programmer has a pair of 4.7K pulldowns, would another pair of 4.7K on the target balance the cable and reduce reflections?

If I remember. Termination with Z0 at one send would reduce reflection. 4.7K and all are seen from the DC side. At 40MHz or 20MHz the Zo would be far less.

3v0 · 13th April 2008, 05:34 PM

Quote:

Originally Posted by mvs sarma

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 · 13th April 2008, 07:48 PM

Hi 3v0,

this long ICSP cable actually works ? wow ...

Petr

mvs sarma · 13th April 2008, 07:56 PM

Quote:

Originally Posted by 3v0

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 · 13th April 2008, 08:20 PM

Sarma,
Not a problem.

Quote:

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 · 15th April 2008, 09:47 AM

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.

http://www.qsl.net/dl4yhf/winpic/ind..._pgc_filtering "

3v0 · 15th April 2008, 10:09 AM

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 · 21st January 2009, 10:16 PM

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.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar
Title	Starter	Forum	Replies	Latest
CD4051 analog multiplexer crosstalk	Mojalco	Electronic Projects Design/Ideas/Reviews	3	20th March 2009 09:00 AM
Using the PGD and PGC pins	UTMonkey	Micro Controllers	9	15th April 2008 08:22 PM
I can't find the PGD and PGC pins on the 16F887...	Krumlink	Datasheet/Parts Requests	9	30th September 2007 07:44 PM

13th April 2008, 04:58 PM	#16
3v0	The cable mod I have SEEMS to be working. I am thinking that if it does not the chance of the shielded cable working is small. Reason is that Microchip claims the problem is reflections rather then cross talk. That can be fixed too but not as easily. __________________ 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, 05:11 PM	#19
blueroomelectronics	Well the programmer has a pair of 4.7K pulldowns, would another pair of 4.7K on the target balance the cable and reduce reflections? __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com/

13th April 2008, 07:48 PM	#22
petrv	Hi 3v0, this long ICSP cable actually works ? wow ... Petr

15th April 2008, 09:47 AM	#25
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. http://www.qsl.net/dl4yhf/winpic/ind..._pgc_filtering " __________________ Regards, Sarma.

15th April 2008, 10:09 AM	#26
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 __________________ 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)

21st January 2009, 10:16 PM	#27
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. Last edited by e_1069; 21st January 2009 at 10:32 PM.