cch (USHORT)
Binary integer with the number of characters received/to be transmitted in the physical device driver receive/transmit queue. This is a memory buffer between the memory pointed to by the READ/WRITE request packet and the receive/transmit hardware for this COM device.
Note: The behavior of data movement between the READ/WRITE request and the receive/transmit queue can change with each release of the physical device driver. Applications should not be dependent on this information.