I guess that should not be an issue...
A half-duplex link can transmit _and_ receive. A half-duplex device will not transmit and receive at the same time.

Maybe you had a simplex link in mind (this is a link that only has a transmit, and no receive..)

So in a half-duplex environment a PC is able to receive data back from the device.

(For clarity's sake: the above does not mean that half-duplex mode will work... That's a question for people with expertise in the T89C51RD2 field... Sofar my expertise is datacomm..)

rgds
Patrick