18f4550 tqfp dedicated icsp pins connection problems

doguhanpala · Joined: 05 Oct 2016 Posts: 120

hello

I have 18f4550 tqfp. I want to program it with icsp. 18f4550 is on a completed pcb and the icsp headers are connected to dedicated pins.

I made the connections, but Pickit 2 can't find the pic. I looked at the datasheet and it says this.

temtronic · Posted: Fri Apr 28, 2017 8:43 am

Obvious question..
Does your version of Pickit2 KNOW about the 18F4550. IF the 4550 was made AFTER the PK2, the PK2 firmware will need to be 'upgraded'.

I use the PK3 and it knows the 4550.

Jay

doguhanpala · Joined: 05 Oct 2016 Posts: 120

doguhanpala · Joined: 05 Oct 2016 Posts: 120

I tried troubleshooting.

At the first section, it says an external voltage detected on Vdd even though i give the Vdd and Gnd from pickit itself. I don't know what is wrong and i skipped that part.
After testing vpp i always get different values. Sometimes it passes the test and gives 12V, other times (%90 mostly) it says low Vpp.

I checked the pgc and pgd with oscilloscope and checked high, low and 30 kHz. The frequency changed to 22, 26 and 28 khz each second. I checked the frequency with 18f2550 and got the same values, so i thought there is nothing wrong with the frequency.

I thought it was a problem with Pickit 2 but i tried the troubleshoot with 18f2550. It passed all the test.

Any ideas about low Vpp voltage?

Note: I tried giving voltage from an external source the low Vpp result is still same.

Ttelmah · Joined: 11 Mar 2010 Posts: 19341

What circuit have you got on the MCLR pin?.
There is a standard problem, that the programmer can only deliver a very low current to this pin, yet has to pull it up to Vpp. Many standard circuits generate too much load on this pin. This is why you will see some of the recommended circuits having a jumper to disconnect the normal connections for programming...

newguy · Joined: 24 Jun 2004 Posts: 1903

To add to what Ttelmah has said, programmers are also quite picky about the load on the PGD and PGC pins as well. I've had to incorporate jumpers on those pins as well.

doguhanpala · Joined: 05 Oct 2016 Posts: 120

Ttelmah · Joined: 11 Mar 2010 Posts: 19341

Yes. The capacitor will stop ICSP from working properly. The Vpp pin has to go up to about 12v to actually do the programming. 4K7 is also a bit 'pushing' the drive capability of most programmers as well. The normal recommendation is to have the resistor/capacitor circuit, and then have a resistor from the junction of this, to the MCLR pin. In normal use the rise time is basically unaffected by this extra resistor (since the input impedance of the MCLR pin is high), but when the programmer pulls the line high this allows a much faster rise time, and lower current requirement from the programmer.

doguhanpala · Joined: 05 Oct 2016 Posts: 120

doguhanpala · Joined: 05 Oct 2016 Posts: 120

temtronic · Posted: Tue May 02, 2017 10:15 am

Maybe an obvious question but can you program another PIC type, say a 16F84 ?

If you can, then your PK2 is working, suggesting the 4550 PIC and/or connections to it are faulty.

Also while you can't program it, can you erase it and confirm it is blank?

Jay

Ttelmah · Joined: 11 Mar 2010 Posts: 19341

The port selection, is not a register. It's a fuse.

Just add ICSP2 to the fuses for your PIC. This selects the second location.
Once set using the primary ICSP pins, this allows further writes to use the secondary pins.
Beware that all your code must have this selected. Though you can't set it using the secondary port, you can clear it using this port, so once selected, the code you write in must always have it set.

Ttelmah · Joined: 11 Mar 2010 Posts: 19341

OK. Lets step back.

You are currently trying to program the chip using the default pins?.

How are you powering the circuit?.
If using the PK2 to supply power, is it going to be able to supply everything needed on the board?. Generally the programmer can only supply a few tens of mA, and if there is any significant circuitry, you need instead to have the board powering itself, and the programmer setup to not supply power.

Have you increased the pullup resistor on MCLR?. 4K7, is lower than is recommended for the PK2.

How long is your cable?.

Also the ICRST pin has to be pulled high if you enable the secondary ICSP port. This is just like the MCLR pin for normal programming.

doguhanpala · Joined: 05 Oct 2016 Posts: 120

Hello Ttelmah

Ttelmah · Joined: 11 Mar 2010 Posts: 19341

The recommendation in the PicKit2 manual uses 10KR.

Once you program the ICSP2 fuse, the secondary port should work. There was mention in the MicroChip site of problems once this is done, unless the ICRST pin is also pulled gently high (10KR again). Problem is that during boot, the MCLR pin is not at Vihh, and so the level on ICRST can sometimes matter....