Hallo,
I made a platine and I mounted a 89S52 with peripherie.
It works fine. I use AEC_ISP and I write in assembler, edit with MP. Now I touched with the measure-pin of the oszilloskop short 230V AC. The platine-mounted 89S52 is ok. The oszilloskop is ok, the PC is ok and my hand too.
But now I can’t use ISP to program: SCK is ok, MOSI is ok but MISO shows not correct picture: The signal goes from +5V to +4,5V (not to GND)
A second made platine shows the same pcture. I don’t know what to do.

I think is it better to connect SCK, MISO and MOSI indirekt and I ask, have everyone the same problem. I were glad to hear from.

With regards
Manfred POMUTZ