register file Select the register file which is suitable for your target uP. The reg51.DAT file is the common file that works for every uP, but ain't got hardware specific registers. You can use this file as a base for your own DAT file.
byte end Specifies the last location of internal memory that can be used by the compiler for storing variables. For uP's with 128 bytes of RAM set it to 70 for example. All space after this value is used for the stack. With the simulator you can test if you run out of stack space. For uP's with 256 bytes of internal RAM, you can use a higher value, F0 for example.
size warning Select this option to enable the compiler to give a warning message when the codesize exceeds the specified size.(decimal)