multiprocessor communication 89C51

Hello everybody,
I am working on a project using 89C51.
one master & 2 slaves are connected & all are set to Mode 3
(multiprocessor).

Slaves are having a some keys on it.After passing the device ID both slaves gets activated & user can press any key.After key pressing slave sends some acknowledge to master.In responce to that master again activates both slaves.

But both slaves consider the key pressing event separetly,what i want is that
both slaves shud consider this event at a time.i.e. even when user presses any key from any slave that shud be considerd as a one event & next time when master activates slave both shud get activated at a time.

can sombody plz suggest any solution to this problem?

What specific uC you use are? Generally, SPI is common use in multi-uC communication.

i am using AT89C51, that does not support SPI or I2C protocols.
I am using inbuild UART from 89C51 ,Communication is done using RS232 Protocol. & 89C51 is initialised to operate in Mode 3.

multiprocessor 8051

check this out, I responded in another thread:
https://www.electro-tech-online.com/threads/master-89s52-send-data-to-another-89s52.25975/