Contents of the SETCOMM.DOC file
DOS offers only partial support for com ports 3 & 4. These two programs,
setcomm.com and set_comm.com allow you to place the base address of the
communications adapter you want to use as a com port. For many programs this
is all you need to be able to use com ports 3 or 4. Usually, it is also
important that the interrupt vector that the com ports use also be made known
to the program. Unfortunately, there are no standards for which vectors com's
3 and 4 use. Frequently, COM3 shares IRQ vector 0x30 with COM1 and COM4 shares
IRQ vector 0x2C with COM2. This information should come out of the manual for
the device you are configuring.
Setcomm.com can be used to list and/or change the com port base addresses.
The syntax is setcomm (port) (address). Use a 0x prefix if the address is in
hexadecimal. Examples, setcomm 4 0x2e8 or setcomm 4 744. If you do not enter
any arguments (i.e. setcomm) the base addresses are displayed and no action is
taken. Set_comm.com is used only to set the port base addresses and does not
print any messages making it the choice for batch files.