Hello, I spent a lot of time to solve the problem but I'm dumb. I modified the INT_ADR_OFF=4000h and the DEF_PC_VAL=4000h and compiled with the following command line parameter install 8 0 0 which means autobaud code start at 0 and xdata at 0. My system has ROM from 0-3fff RAM 0-3fff as xdata and 4000-7fff as user code area. When I started to try the monitor id didn't work. The connection was succesfull but when I try to download a program I get an error message there is no RAM at 0. The PC value on the screen was permanently 0600h and when I tried to reset from the reset button on the screen it showed 600h again. Help me please. Cheer George