Thanks Peter for the reply.My problem is i need to control the RTS pin too using the printer.In the datasheet it is mentioned as thus XON / XOFF Transmission timing - XON (11 H) Transmission • When the receive buffer is released from the buffer full state (49.5KB) - XOFF (13 H) Transmission • When the receive buffer becomes full(50KB) • When an error has occurred.