Technical information

NewBIOS Reference Serial Solutions
Service AFH, Get/Set IRQ Line.____________________________
Compatibility._____________
NewBIOS service only, ignored by PC ROM BIOS.
Parameters.___________
AH = AFH Denotes service AFH
DX = 0...31 Port number, 0=COM1...31=COM32
AL = 00H Denotes read IRQ line
AL = 01H Denotes write IRQ line, and
BL = 2..15 IRQ line 2..15 (-1 means no line)
Return Values._____________
BL = 2..15 IRQ line used (-1 means no line)
Meaning._________
Service AFH is used to read or set the IRQ line used with
a particular port. NewBIOS does not use these values but the
NewCOM.SYS device driver does use them. On a read the value
of the IRQ line for the port is returned in BL, and on a write
the value in BL is used to set the IRQ line used with the port.
It is best to set the IRQ line on the NewCOM.SYS line
in the CONFIG.SYS file using the /I command for stand
alone serial ports and the /L command for interrupt sharing
multiports cards.
Other Points.____________
NewBIOS allows the setting of IRQ lines for ports whose
address has not yet been set, but their address remains zero and
they cannot be used. An IRQ line value of -1, = 255, means ’no
IRQ set’, and forces NewCOM to use polled I/O for that port.
Figure 5-2. Interrupt Allocation.____________________________
Chapter 5 Page 93