Thanks for the practical solution for my problem, for the theory behind it I have to start studying:
what I do not understand is that sending 0x01 (or other hex-values) does not give a problem (as being a hex-value for data) while 0x00 is not accepted as hex-data.
As PaulS stated ''The value 0x00 is not typed'', my (study)problem is then why is 0x01 ''typed''
or differently: if I have to declare 0x00 to be a byte ((byte)0x00),
why is it not necessary to have 0x01 also to be declared to be a byte ((byte)0x01).
I have just read the answer of PaulS on Professor Chaos: I have to admit it is above my knowledge-level.
Therefore again: thanks for the help. Jan.