Although the Maplin programmer will work with most PCs there are a few that just don't want to play ball. The most likely cause is the parallel port hardware (to learn more about PC parallel ports in general see Jan Axelson's Parallel Port Central or Warp Nine Engineering's information on the new(ish) IEEE 1284 standard). Tim Forcer decided to work out why his programmer wouldn't work on a PC equipped with an IEEE 1284 port. Based on some experiments he modified his programmer like this:
LPT Port ribbon cable to Programmer to Programmer
D type pin component
_____
D0 --------------------- 2 -------[_____]------+--- IC1 pin 9
470 |
__|__
150p _____
|
|
///
_____
+---[_____]---> +5V
| 1200
|
D1 --------------------- 3 ----+------------------- IC1 pin 5
D2 --------------------- 4 ------------------------ IC1 pin 1
_____
D3 --------------------- 5 -------[_____]------+--- IC1 pin 3
100 |
__|__
150p _____
|
|
///
_____
+---[_____]---> +5V
| 1200
|
/ACK -------------------- 10 ----+------------------- IC1 pin 10
The components are soldered onto the Maplin board and the tracks from the D-type connector pins 2 and 5 to IC1 must be cut to accommodate them. The additional components needed are one 470 ohm, one 100 ohm and two 1.2k resistors plus two 150pF capacitors. If you don't want to cut the tracks it may be possible to put the 470 ohm and 100 ohm resistors inside the hood of the 25-way connector - I suggest you only do that if you have dedicated the cable to use with the programmer.