Hi all, i've a really strange issue with a DALLAS DS89C430 full 8051 compatible chip. I've an app. with external program memory, and external sram (both 70ns acccess time, clock is 25mhz). When i compile my code with C51 7.1 or 7.5, everithing work, i can see a led blinking, i can see chars coming out from the UART0, filling SBUF0, but everytime in my source code i use something like *p++ , or a=tab[5], it don't work, or better, strange chars are read out, not the cortrect one. If i put in the same socket a DS87C520, slower but similar chip, WITH THE SAME CODE, everything works correctly. Anyway, i don't think is a memory access issue, since i've measured with the scope, the memories give data correctly inside the PSEN time. So, seems an op codes compatibility issue, or a bad adressing, or even, a wrong place adressing. I would be happy even for some suggestion, Infinite thanks. Angelo