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16F PIC DIY Programmer troubleshooting

I'm designing a programmer for my 16F88 and I almost have the engine complete. I'm running into one bizarre issue that I can't seem to trace down. I'm hoping for some troubleshooting advice.

The programming spec says to write a 14-bit word by cycling the clock

16 times and latching the word onto the 2nd through 15th cycle. Likewise, reading a 14-bit word involves cycling the clock 16 times and reading the 2nd through 15th bits. The 1st and 16th bits are always pads. I've noticed that my PIC always uses 1's to pad the 14-bit word during a read command.

My issue arises when the MSB of my 14-bit word is not a "1". When I try to read a word whose MSB is "0", the PIC doesn't throw a "1" as the

16th bit and then fails to read any more addresses. If I attempt to increment and read beyond that troublesome word, it always returns 0x3FFF.

For example, if my 14-bit word is b00000000000001, then the PIC returns the 16-bit value of b1000000000000011 and everything is great (I just grab the 14-bits between the padded 1's). However, if my word is b00000000000010, the PIC returns b1000000000000100 and everything fails after that (it didn't throw the last "1" as the 16th bit).

I confirmed my write procedure is correct by incrementing past the troublesome word and continuing to read. In other words, all the data is being written, it's just not being read correct.

I'd appreciate any toubleshooting advice. This problem has been perplexing me for a while now.

Thanks!

-Dan

Reply to
Damn Dan
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I just programmed my 16f88 the other day, using about 5 resistors conected it directly to the serial port (much like the com84 design) and winpic software. although you might just want to build one for yourself for fun/torture it might be an idea to see how the bits are sent with a working programmer considering how simple it is.

Colin =^.^=

Reply to
colin

messagenews: snipped-for-privacy@k70g2000cwa.googlegroups.com...

using about 5 resistors conected

Reply to
johannesnehls

The comm84 design is on the web somewhere, it realy is so simple though, i just conected resistors from the various rs232 ports to the various pic pins,

tx from the pc rs232 port =pin3 on a 9pin connector, goes to mclr|vpp via

4k7 resistor, dtr =pin4 goes to pgdata|rb7 via 2k2 resistor, cts =pin8 goes also to pgdata|rb7 but with no resistor, rts =pin7 goes to pgclock|rb6 via 10k resistor, gnd =pin5 goes to gnd.

its basicaly the absoulute minimum needed.

The only issue is that it relies on the pc port giving a good healthy +12v output some laptops only give 8v wich isnt enough, however you could use low voltage prgm mode, also the input threshold of the rs232 must be slightly positive wich again on some laptops isnt, an alternative is to conect the rs232 gnd to about 2 or 3v with repsect to the pic gnd this shld help with both propblems, this means you mustnt earth the gnd of the pic. it worked fine with my desktop and pic16f88.

this link gives the same thing but with a few bells and whistles such as providng 5v to the pic from the rs232 port and some protection diodes etc:-

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Im going to try it on a dspic30 in a few days, however ive seen a circuit wich duplicates the icd2 directly alowing debugging so i might build that or if im feeling lazy i might just buy one, but where the fun ... it does however require you to program a picf687 so its like pulling yourself up by your shoelaces ! i might go for the usb version too as ive only got one rs232 port.

Colin =^.^=

Reply to
colin

actually this was the link i got the simple idea from but to add some resistors,

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Colin =^.^=

Reply to
colin

the

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Wel ive just bought the PICKIT 2 STARTER KIT cos it seemed quite good value considering the cost of the components to build one.

Colin =^.^=

Reply to
colin

. col>The comm84 design is on the web somewhere,

Yup.

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(It helps if you spell it the original way.)

Reply to
JeffM

Oops, well I did spell it the right way in my original post.

Colin =^.^=

Reply to
colin

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