There has been, I do not know how many, posts "this 'proven and tested' programming circuit does not work for the 8253" DO spend the $25 and get the 'authorized' cable from Atmel.

I am NOT saying that 'none' works, just that, in my opinion, too many has been down the garden path and had to give up and spend the $25 after musch wasted effort to save it. DO note that, some circuits that has been posted as 'do not work' has been refuted by others as 'do work'.

It seems that every kitchen table circuit for programming these chips is done by "I think this will work, I'll test it, and if it passes the test I'll post that it works" not by "this circuit is designed based on Atmel specs to work guaranteed".

I do not do Atmel, but reading the posts on this subject, I think to have seen that the issue is that Atmel do not release complete specs on this particular issue.

Erik