Michael Kern wrote:
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I believe in one of the following:
1. There are internal lock bits / fuses for security purposes, wich should inhibit reading contents of internal memory by a program in an external eprom. (There are some hints in the data sheet, but not very clearly, and I couldn't work it out)
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Mike,

I consider this the problem, too. But then, running FLIP to read the contents of HSB
tells me, that the three relevant bits (LB0-2) are set to one resulting in "No program lock features enabled", according to the datasheet section 8.4.2.2.
I tried to alter some of the bits in HSB, but to no avail, register contents always is displayed as FFh, as are the manufacturer and device id's as well, by the way.
I'm gonna let you know, whether I get any further on this.
Thanks to you and everyone that tried to help!
-uwe