try running the rig at 1200 baud both ways and see what happens

As I had mentioned earlier, we are using 12 Mhz crystal in master, and are using Serial Communication Mode 3 of 8052.

With these specifications, the available baud rates in decreasing order are:

31250, 15625, 7812, 3906, 1953, ....

With our initial setup with 31250 baud, there are software delay loops in addressing slaves and waiting for acknowledges. The errors (E1 - an addressed slave failed to send end of data) used to come at a variable rate.

In the same system, we substituted the software delays with 'waiting in while loop with software watchdog breakpoints', and the system became very fast
Sometimes, the system used to hang or even failed to boot.The error E1 rate is also more.

We had tried 15625 baud, but there is not so much decrease in the error rate.

We had implemented 7812 and 3906 baud rates. We had also added the code of sending 'no data byte' before the end of data byte from slave to master.

What we noticed is that the errors are very less in both the rates, but the operations in the system are very slow with 3906 baud.

So, we are now using 7812 baud only.