This a FREE tool chain which compiles C codes into 8051 binary code, converts the binary to RTL ROM, and simulate in Modelsim.
SDCC is the compiler.
Example compilation:
cd compile
sdcc --IRAM-size 0x80 --xram-size 0x800 t8051.c
REM sdcc --IRAM-size 0x80 t8051.c
packihx t8051.ihx > t8051.hex
..\test\mkrom.exe ..\compile\t8051.hex
