Vpp generation failed - SX18AC

juggler

I recently purchased· a few SX chips, including the smaller 18 pin chips.· I seated·one of the SX18s·in my professional development board and uploaded one of the example programs.· It loaded fine, and I read it back fine.·

Now, a week later I've written some code to test out, and when I tried to download it to the chip, I got:"Vpp generation failed".·

So I took a step back and just tried to read what's already there (using the Run->Device->Read)·- I get the same error.· I had a SX28 lying around, so I plugged it in and tried to read it -·it read it fine.

Finally, I pulled out a shiny new SX18 that was still in its packaging.· I tried to read from that one, and got the same "Vpp generation failed" error.· So, it seems like it·may only a problem with the SX18s.· I searched this forum for the error, but nothing came up.· I searched the web and found several hits, but none listed a solution.

I'm running SX-Key V3.10 on WinXP SP2.

Any help would be much appreciated.· Thanks.

Rsadeika

I take it that you are using the·new Parallax professional board. I believe that the SX socket on the board only works with an SX28 chip. If you look back in the posts, I think their was a discussion about a simillar issue.

Guenther Daubach

juggler,

I wonder how you got programmed the SX18 at first place. The socket on the professional development board is designed for the SX28 chip, and the SX18 has a differrent pinout.

The pins required for programming are Vss, Vdd, OSC1 and OSC2. On the SX28, these are pins 4, 2, 27, and 28 where on the SX18, these are pins 5, 14, 16, and 15. In addition, the /MCLR pin must be pulled up to Vdd, which is pin 28 on an SX28 and pin 4 on an SX18.

IOW, you can't insert an SX18 into the PDB's socket that is designed for an SX28. Be aware that in doing so, you might even damage the chip, or the SX-Key.

The only way would be that you build an adapter. I'm not sure if you have an SX18 datasheet available, or my book, therefore, here is the complete pinout for the SX18:

1 = RA2
2 = RA3
3 = RTCC
4 = /MCLR
5 = Vss
6 = RB0
7 = RB1
8 = RB2
9 = RB3
10 = RB4
11 = RB5
12 = RB6
13 = RB7
14 = Vdd
15 = OSC2
16 = OSC1
17 = RA0
18 = RA1

You can find the pinout of the SX28 in the datasheet available at the Parallax site.

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Greetings from Germany,

G

juggler

Rsadeika,

Thanks for your reply. I also have the SX Tech programmer, and I just tried it and get the same error when I use that. While searching for the post you mentioned about the PDB and SX chips, I came across this thread:

http://forums.parallax.com/forums/default.aspx?f=7&m=83563

in which Ken stated that the SX Tech board cannot be used to program Sx18's because of pin differences when compared to newer chips. In fact, one poster on that thread had the same error as I mentioned before (but it did not show up in my search). I'll try Ken's suggestion of using a breadboard and wiring the connections up myself.

This is all strange, though. I know I programmed this thing (SX18) with one of my two boards!

Edit:

Guenther,
Thanks for your post as well.· I must have been working on mine when you posted.· Hmm... maybe I dreamed about programming the SX18 after all?!· Once I wire up a breadboard to connect to the SX18 I'll read it's contents and see if it's blank.· I'll be sure to update this post.

Thanks again!

Post Edited (juggler) : 8/13/2005 8:26:14 PM GMT

Guenther Daubach

Hey Juggler,

usually, the SX-Key IDE reports a "Vpp generation failed" message, when there is too much load on the line going to OSC1 as during programming, this line is pulled up to +12V. This means that the SX-Key usually applies this voltage to pin 27 of the SX28 socket but when an SX18 is sitting there (assuming that it is aligned with the socket's pin1), the voltage is fed into the SX18 pin 17 (which is RA0) - not too healthy . On the other hand, pin 5 of the SX18 (Vss) remains floating because on the SX28, this is a n.c. pin, so this may be the reason why your "experiment" did not frie the SX18.

Good idea to wire up the "adapter" on a breadboard, this should work fine, and you only need to route the four pins I had mentioned in my last post. In addition, don't forget to pull the /MCLR pin to Vdd (a 4.7 kOhm resostor would be fine). Otherwise, the IDE will com up with another quite popular error message: "Chip connection failed". Recently, I had to learn this lesson once again when testing a new SX project.

When you have the breadboard done, I really wonder what results you get when you read out the "programmed" SX18 - should there be anything else but tons of $FFs, this might be good for another entry in the Guiness Book of Records.

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Greetings from Germany,

G

juggler

I completed the wiring setup and read in the data from my SX18 - All $FFs. I'll check myself into a mental institution later today. :P I guess I did everything with the SX28s and for some reason thought I had used the SX18s.

Sorry about the false information, and thanks for helping me get setup to program my SX18s!!

Guenther Daubach

Hey Juggler,

no need to visit a mental institution - errors are there to be made. A couple of days, I breadboarded a special system for SX28 programming. When I tested it, the SX-Key always reported the famous "Chip connection failed" error. I went through all the suggestions I have compiled in my own SX FAQ text about that error but could not find the problem. Until I noticed that I had soldered the resistor for pulling up the MCLR/ line to Vss instead to Vdd with the other end - Arghhh.

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Greetings from Germany,

G