propblem with RS232 to RS485 Pleased help!

[anhnha]

Hi all,
I had do the circuit like that.But I wire up in breadboard it is not work.In my project I need to communicate between computer(COMM PORT) and micro.But now I want to check 2 circuits that I had wire in breadboard:
-the first breadboard for RS232 to RS485
-the second breadboard for RS485 to RS232
in reality, I need 2 computers to communicate but now have only one therefore I used TX pin of comm port to transmit and also used RX of this port to receive data.
Because I only used on computer thus I had connect TX of comm port to 232 input of one breadboard and RX of comm port to 232 output of the other breardboard.And then I used the program i posted above to transmit and receive data from comm port.But when I am not use 5 Voltage connected to ICs and I supprised due to is read from comm port is exact but when power is connected then it is not work.At first I think that it receiced data may be TX and RX is connected to each other but when i used ohm meter to measure the resistance between TX and RX, i received the value is very large and this mean it is not connected.I am confused why it is not connected but i can received data and when power is connnected it is not work.
I have checked all connected in breadboard, all of them are good.Would you give me how to solved it,i have wire up the circuit in breadboard many times but all are the same.Finally I can not to transmit between two computer.Will i need add something in this circuit in reality?Are there anything wrong in my schematic?
would you help me check it.I have attach my file in this

[anhnha]

And this is orginal circuit I had used:
http://www.bb-elec.com/bb-elec/liter...tbr-3903ds.pdf

[cnc_4_me]

The easiest thing to do is follow the signal through with a logic probe.

[Chazzmiester]

I think you are talking about a 'cross-over' arrangment? ie tx from computer 1 to rx on computer 2 and tx on computer 2 to rx on computer 1? We use pre-fabbed 'Cross-over' cables to network directly with another computer or printer for 2 way communication, other wise you need a router, switch or hub in the middle to do the tx\rx dance.

hth
Chazz