If your board for example has a 65c22 you can use one of its two ports, see
http://www.westerndesigncenter.com/newpages/W65C22.html
But you sure need to write some software! And for the development you really need a logical analyser to make the I/O visible.
I interface the PC to 65C22 over the parallel port and corresponding "hand-shake" software I have written and can make available.
There are several assemblers available! I use an assembler that I have written myself (in FORTRAN, i.e. OK for a LINUX system as well as for Windows). At least for me this is the best as I know exactly how it works and can adapt the interfaces to exactly fit my setup. If you want to use my assembler I can make it available!
Otherwise Daryl's assembler is quite good (good diagnosis). That it does not support the new opcodes is not really a problem, they are not too useful anyway! See
http://65c02.tripod.com/ from where this assembler can be downloaded together with complete documentation (or was it removed? Put it back, Daryl!)