xPC Target 4.1 (R2009a) supports A/D, D/A, Digital I/O, counters and incremental encoders for National Instruments M Series Boards PCI-6251 and PCI-6259. PCI-6120 is not supported by xPC Target.
Refer to link below to get a complete list of supported hardware for xPC Target 4.1 (R2009a):
<http://www.mathworks.com/products/xpctarget/supportedio.html>
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