hi,
There are two types of parallel programers I tried during my work with 51s:

1) programer do not start programing if wrong device is selected. First of all, it reads the signature of a chip inserted; if it is not correct for device selected, then programming does not start.

2) programmer does not read signature. It starts to programing with algorithm of selected device. Usually it fails at check point after the first block of data has been wrote due different devices has different algorithm/setup pins and signals.

I have checked my database and found that S52 has different pins` programming setup from both C52 and S8252. So it seems original poster has selected correct device due programing.

Regards,
Oleg