Hi Ijaz,

Thanks for your reply. my micro refreshes the relays every 2ms. that is the time taking to complete one cycle in while loop. but the CPU is completely hangs.

i am sorry i amy not be able to post the schematic and layout because it is commericial product.

My hardware is

Processor : F124
Speed : 49mhz

32 Digital inputs
46 Digital outputs
8 analog inputs 0-2.5V


when i use io's as weak pull up only then frequency of the hang is very less.
but i have to use push pull mode for speed to access inputs and outputs on the bus.

Port 4 to 8 bit data bus via '245.
input card have 5 '245 connected to bus via one '245
output card have 4 '574 and one '245. it also connects to bus via '245.

other port pins are used to drive the enable line for '245 and '574.

i hope this will give some idea about the hardware .

Thanks and regards.

Haribabu