Well this thread has been interesting. Both conventional and non-conventional solutions have been thrown up and I now think it is the OPs discreetion to choose the required path.

Prahlad's scheme may work if,

- The setup is one off and non-commercial in nature.
- The OP has a clear idea about bit banged RS232 implementation and is well versed in writing both the PC end software and MCU firmware.
- Missed bytes will not bring the roof down!

Yes all such non-conventional solutions do come with a few riders and it is important the designer is wary of the pitfalls.

The other option to go with multi drop RS485 would be the way to go if,

- The setup is for commercial use and warranty has to be addressed, even for 1-off quantity.
- Missed data bytes cannot be tolerated and the application is critical.

Once the above decision is made, then it will boil down to economics and availability of required modules. And if in this process, the outcome is contradictory ( customer willing to accept non-conventional solution but wants all the benefits of custom solution ) then bid goodbye to the project. I am sure it is very safe that way.

Raghu