"Have you had a look at ALE pulses? Do they look good, in terms of ringing and edges? ALE signal should not have to run a long distance to DS1232."

Yes I did and noticed it is not very sharp on the rising edge. Kind off rounded there. (The ALE connects to the DS1232 via a 11mm approx. long track )

What can this rounding of edge be due to ? In fact in the absence of a benchmark ALE pulse, I do not know how far I am away from the true one. ( The ALE is connected to the DS1232, 74hc573 ( 2nos ) for address latching.)

Also noticed this : With the DS1232 removed and powered up, the ALE from the 89c51rd2bn is at 1MHz ( 6 Mhz Crystal and 6 clock mode ). But when a high pulse is applied to reset pin, the ALE siwtches to 2 MHz and the system works. Whether this points to a probable cause - well I am quite tired to figure out right now. But maybe it rings a bell for someone ? ( In any case my client is all set to ring my bell if the unit is not back with him tomorrow...)

Raghu