Thanx 4 responses.

To Joseph,
No other equipments (I tested) sends this kind of reset etc commands. They only send data that gets printed through whatever settings printer has.
Also I tried on 3 of equipments of same make & model for which hanging problem is seen; behaviour is same. Also this problem is not seen if actual printer is connected to this equipment

To Stefen,
nAck is normally high & gives -ve pulse at every byte received. SEL is at logic 1 (4.9V).

Regards,
Mahesh