I have quite recently started working with uVision and an Atmel MCU, and I think that I may have done something wrong in my settings... Here goes: The problem is that both RD and WR goes low when I try to read or write. My hardware is an Atmel T89C51RD2 MCU, and it doesn't matter that I set the AUXR register EXTRAM bit to one - the RD/WR toggles and both are low at the same time. My code looks good enough; the write cycle assembler code looks as follows:
C:0x0015 9098FC MOV DPTR,#addressbyte(0x98FC) C:0x0018 7401 MOV A,#0x01 C:0x001A F0 MOVX @DPTR,A
Anybody out there that knows if it is normal that an mcu has 1V output low voltage? I have never checked on the few projects I have worked with, but it seems rather high, doesn't it? Specially since the data sheet says max 0.45V. if you see anything that differs fron the datasheet, you can be sure that eithet your circuit or the chip is bad. Is the 1V measured relative to the ground pin rather than some arbitrary ground point? What is the low output voltage (measured as above) if the pin is not connected to anything. Do these two simple tests they may be educational. Erik