hi all,
here is very simple code which is not working on AT89C2051 mcu


port1 data 090h
port3 data 0b0h
sp data 081h
ie data 0a8h
tcon data 088h
psw data 0d0h
b data 0f0h
acc data 0e0h
tmod data 89h
tl1 data 8bh
th1 data 8dh
tl0 data 8ah
th0 data 8ch
dpl data 082h
dph data 083h
scon data 98h
sbuf data 99h
led_data data 20h
status data 2fh

org 0000h
ljmp program_start ;bypass interupt table
org 0030h
program_start:
mov port3,#0ffh
mov port1,#0ffh
mov r0,#7fh
fill_zeros:
mov @r0,#00h
djnz r0,fill_zeros
system:
jb port3.2,system
mov port1,#00h
here:
sjmp here
end
when i press switch on port3.2,whole port1 should go low but nothing happenes port1 remains high,but if i remove ram clearing code
mov r0,#7fh
fill_zeros:
mov @r0,#00h
djnz r0,fill_zeros
program works fine i think problem is with ram clear code what where is problem i am unable to find as code works in simulator.
shivnai