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