BIOS INT 14H Example Needed

[Jim Boyle]

I am trying to use the BIOS serial communication services provided
by INT 14H. I do not seem to be able to get a small assembly language
program to work. I am new to embedded assembly language programming
and would like to know where I can get some example source code
which uses the INT 14H BIOS service. I am programming at the BIOS
level, no DOS services are available.

Any information is appreciated.

Jim Boyle
boy...@dave-world.net

[Dave Baldwin / The Computer Journal]

INT 14h BIOS services for the PC serial ports are very limited. They are
not interrupt driven so they don't buffer the characters. They also
require you to use the handshake lines. Most people write their own
routines to directly access the serial ports. Source code to do that
along with datasheets, application notes, and links to related info is
available on TCJ's "Asynchronous Serial Data Communications" page. Go to
"http://www.psyber.com/~tcj/" and click on 'Serial Com'.

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[James V. Boyle]

Thank you, Dave and Peter, for your assistance. The problem I was
having with INT 14 was two-fold. First I did not conceptually
understand how the four services should be used. The documents
from The Computer Journal site were most helpful especially the
not that DSR needs to be asserted for read operations to work. This
note is not stated in the Phoenix BIOS text I have.

Second, the other information on handshaking for writes completed
the picture. I now have a working assembly language program which
communicates at 9600 baud.

Thanks again the assistance.

Jim Boyle