Tom, thanks for the advise. I bought a 16F84, programmed a few 1's and 2's:
the result was the same as with the 12c508.
I got a brand new programmer from my distributer, still the same problem.
So, the problems are caused by faul communications with the parallel port of
the 286 computer. A known problem??

Leo van Loon

-----Oorspronkelijk bericht-----
Van: Tom Handley <thandley@TELEPORT.COM>
Aan: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Datum: donderdag 29 januari 1998 13:04
Onderwerp: Re: Problems with Parallax programmer


>  Leo, I have the Parallax programmer which included the cable and
>power supply. I assume you had to `roll your own'. The first thing to
>check is that you are running SPASM/SPEP v4.7 and have the right
>firmware chip. It looks like you do since you can program the 12C508.
>The next thing I would check is your connection to the Parallel port.
>Keep the cable as short as possible and make sure you have a good
>ground. Have you tried programming a 16C/F84? If that works, your
>interface should be fine. Are you sure your 12C508 adapter is wired
>correctly? I made a simple 12Cxxx adapter mounting an 8 pin DIP
>socket on a 28 pin DIP header. It works fine. I normally have the
>40 pin adapter connected to the 26 pin header on the programmer
>board but if you want to use the header the connections to the
>12C5xx are:
>
>      (looking at the board with the header to the right):
>
>      Header   12C5xx        RTCC o o MCLR
>      ---------------        Vdd  o o OSC1
>      Vdd      Vdd           Vss  o o
>      Vss      Vss                o o
>      MCLR     MCLR/Vpp      RA0  o o
>      RB6      GP1           RA1  o o
>      RB7      GP0           RA2  o o
>                             RA3  o o
>                             RB0  o o
>                             RB1  o o
>                             RB2  o o RB7
>                             RB3  o o RB6
>                             RB4  o o RB5
>
>   Finally, if you are running Windows 95, try restarting in the
>MSDOS-Only mode.
>
>   - Tom
>
>At 02:52 PM 1/27/98 +0100, you wrote:
>>Hoi!
>>
>>As beginner in PICworld I bought a Parallax hobbyist programmer.
>>I can program my 12C508 PIC's but only sometimes with a 'device
programmed'
>>result. Reading, verifying and erase check have every time another result,
>>often with 'NO PIC-PGM DETECTED' as result
>>
>>I use an AT-PC with standard parallel port for programming. I have the
>>impression that communication between PC and programmer is not correctly
>>timed.
>>Is there anyone with the same experience and the solution for this
problem?
>>
>>Leo van Loon
>
>