Erik Malund wrote:
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the '243 is a parrallel bus multiplexer and you talk about a "THE serial .

Hi Erik,
74LS243 is quad transceiver (3-states).Though it is used with the parallel bus but I wired experimentally with the serial bus alloting 3 drivers each for tx & rx side,in order disable the serial bus from the slaves to avoide crosstalk but the moment I give it power the '243 gets heated and when serial communication is allowed the situation worsen .I have now changed the design with the AND gates i.e two drivers each for TX & RX side to share the load hope this will work .what do you suggest?

Thanks
Sanjeev