+----+       +------+
|    | RS232 | 8051 |             Bus
| PC +<----->+ Coms +<======+==========+==========+=====>
|    |       | proc |       |          |          |
+----+       +------+       |          |          |
                        +---+--+   +---+--+   +---+--+
                        | 8051 |   | 8051 |   | 8051 |
                        | slave|   | slave|   | slave|
                        +------+   +------+   +------+