Format of COMM-DRV port control block:
Offset	Type	Description	)
 00h	WORD	port IO address
 02h	WORD	port IRQ
 04h	WORD	baud rate
 06h	WORD	parity
 08h	WORD	data bits
 0Ah	WORD	stop bits
 0Ch	WORD	break status (0000h off)
 0Eh	WORD	flow control protocol
 10h	BYTE	input block
 11h	BYTE	output block
 12h	WORD	low threshold
 14h	WORD	high threshold
 16h	WORD	segment of buffer
 18h	WORD	offset of buffer
 1Ah	WORD	input buffer length
 1Ch	WORD	output buffer length
 1Eh	BYTE	auxiliary address
 1Fh	BYTE	spare
 20h  4 WORDs	spares