I assume you have installed your driver into the system. When you run HyperTerminal you must configure connection so the
program would use your driver as a target device.
At start HyperTerminal will send a read IRP (IRP_MJ_READ) to your driver in other words it will start listening for any data.
If you complete this read IRP immediately, the application will send consecutive reading IRPs.
When you press keystroke on the keyboard the Write IRP is issued (IRP_MJ_WRITE) and sent to the driver.