Hello Uwe,

I've got exactly the same problem with a RC2 based T89C51CC01!

I assume, that the content of any internal memory is not the reason of this behavior, because /EA is Low. I tested it with all kinds of contents of the external eprom, but reaction was always the same. I even used several crystals down to 1 MHz, but, still the same...

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)

2. I heard about a encryption unit in the philips micros and found a hint int the 87C591 datasheet. Maybee there's one even in the RC2 and CC01 devices, and its activation causes the chip to behave in this way. (Rather unlikely, but it could be)

I am working many days on this problem, and couldn't solve it yet. I even bought a parallel programmer with plcc adaptors to do a full chip erase, but, without use. As you described, the hardware is working well with other micros.

I've got a really big problem with this: any substantial help is more than welcome!

Mike

PS: I know about the flash, and I'm able to program it, but I need the external memory! (Its not the problem why I need it, its a big problem that I can't use it)