Thanks to all for valuable reply

Kai I will try to convince senior to use seperate time base generator for each,but in case, is there any other solution to reduce hardware

Deatils of application in which I am using 12 controllers r as follows

It is for Lap counting & time measurement for each lap
for Go_Karting track.

Max kart no. is 12
any no. of karts can pass finish line simultaneously

I am using 12 RF tx-rx pairs with different frequencies in range of 27MHz(6 crystal pairs)

each receiver will interrupt controller whenever kart will passs start/finish line.

13th controller(commer) is used to communicate with pc collecting data from all counters & sending it to pc

all r communicating over serial port.
To seperate pc-commer link from counters-commer link
switching device is used wchich is controlled by counters.

If commer finds line free && new data received from any of counters it takes controll of link & send data to pc.

It works well but after increasing no. of controllers to 4 I faces a problem of deviation in consecutive reading with interrupt at same frequency. deviatoin is at 100th of a second position. all other higher digits r constant

hope to get reply
Thanks