Erik, no problems with your comments. I too agree. The lm628 obviously has some weird bus timing that is probably easily overlooked. The control signals look normal so a quick lash up to the 8051 seems simple.....until you read the specs! So K.ganesh, you will most likely have to write to this devices using a sequence of instructions to control the ports rather than use a movx a,@dptr method. Or as Erik suggested, use external data latches etc. I think this will go some way to resolving your problem.