INT 53 - Tandy 2000 - SERIAL COMMUNICATIONS                                     
Note:	this interrupt is identical to INT 14 on Tandy 2000
SeeAlso: INT 14/AH=00h"SERIAL",INT 14/AH=01h,INT 14/AH=02h,INT 14/AH=03h
SeeAlso: INT 14/AH=04h"Tandy 2000",INT 52"Tandy 2000",INT 54"Tandy 2000"