RTX-51 is a runtime library that, together with C51, allows real-time systems to be implemented for all processors of the 8051 family (e.g., 8051, 8052, 80515, etc.), except for the 8?C751 and 8?C752. RTX-251 extends the functionality of the RTX-51 to the new intel MCSÒ 251 family of processors. It is available as a set of runtime libraries supporting the binary and the source mode to be used with the C251.