Sebastian,

Nobody wants to do a bunch of research just to understand what you're asking. Please be more specific about the nature of your question, and provide a schematic diagram, not of the PJRC board, but of the portion you're using and EXACTLY how it is being utilized. Maybe, then, someone can help you figure out what the problem is. Further, you should probably provide the assembler output including the error messages, rather than a source listing.

When you say "Port A," what do you mean? Is it a port on one of the i8255's? Which one?

When you say, "I just need to use the less significant bits (0 to 3)," do you mean that you have been assigned to write the code using 4-bit interface mode?

You complain that, "I can't compile it due to a Syntax error in line 50," but you don't provide line numbers, AND you don't say which assembler (You aren't compiling anything, since you're presumably using an assembler!) is giving you that error message.

I don't see what's wrong with the 50th line,

cjne @R1, #01, msg01

Some assemblers insist that you specify the constant's radix, though, even when it's unimportant, in that 01b=01o=01d=01h. I have one such assembler (ASEM-51) that requires it on some instructions and not on others, which I can't explain.

RE