Yes, that's what i meant. But a data exchange b/w controllers can be done easily done using 3 i/o lines but with some more overhead because of s/w control of signal flow.

For instance, it can be done by connecting one of external int of both controllers together and sharing the c/d and Ack signal.
Now uC1 is having some data of serial to communicate with uC2.

uC1 first must disable its external interrupt, generate a int to uC2 with the corresponding signals and command word. Wait for the acknowledge from uC2 and release the int, bus and other signals.


This way it can accomplished.

V.Nagarajan.