three things:
(1) the XOR node in vvvv doesnt do what you like it to do - the vvvv node XOR will just work with single bits, conrad wants you to xor all 8 bits from the incoming bytes (a so called bitwise xor). So you could use Radix to split the byte into 8 single bits, XOR these, and use another Radix to get everything back into one byte.

Or - and this is much easier - you could use the Expr node, which also features an operation called XOR, which is exactly that type of XOR you´re looking for.

i know both nodes should be able to deal with both definitions…

(2) there are diffent ways for converting numbers into the strings for the RS232 node - each device seem to invent its own style. from the BASIC code provided in the conrad manual i see that they are using the chr$ function. To emulate that, use SpellValue in ascii mode.

and (3)
i dont understand the framedelay before the xor - better remove that…