DOS / Interrupts / Int 2F / 12/20


                    DOS INTERNAL SERVICES - Get DCB Number

Input	DOS1	N	DOS2	N	DOS3	Y	DOS5	Y	Output
AX	12h		20h		Error Code				AX
BX	File Handle								BX
CX									CX
DX					Pointer to DCB				ES:DI
ES:DI					Set if Error				CF