hi, i've some trouble after a firmware update procedure, some like a stack misalignment o something strange... i'm quite newby, working with 8051 family from 4 mounths. I try to explain the trouble, please forgive my bad english. i'm using a Ds89C420 with 16kinternal flash, but my main application run from an external 29F040. When i want update this external flash, trhough a win application with a little protocol i write trough serial port some escape sequences, (i think is a quite std fashion). From the esternal flash i switch to internal changing ROMSIZE (that's is done reading carefully the ds89c420 manual specification for this particular register change) and then jump at address 0 of the internal flash. After that, from internal flash i rewrite the external flash in 512byte bloks. After the update is completed, i change again ROMSIZE and i perform a jump back in the external flash, and so the main application restart. This procedure works quite fine, but at the restart ot the main updated application, the hardware stack seems in some way corrupted: At the first call of a function like this: unsigned char xdata * Int2Char(int param) { static unsigned char cb[8]; .... return &cb[3] } the pointer value before and after return are: before : x:8f6c after : x:016c And Seems that after this software reboot the "return" for general pointers won't work anymore. Every kind of help or redirection is very appreciated. Thanks Angelo