parallel port in DOS under XP

[Rick Merrill]

C code can ACCESS the "parallel port" in DOS under XP,
BUT the output written only SOMETIMES is the same as
can be read back from the output port (with nothing
plugged in). Pretty odd. How do you explain it? - RM

 

[Si Ballenger]

C code can ACCESS the "parallel port" in DOS under XP,
BUT the output written only SOMETIMES is the same as
can be read back from the output port (with nothing
plugged in). Pretty odd. How do you explain it? - RM

Unless you have gotten user level access to the parallel port
hardware, you probably aren't really controlling the hardware.
You are just seeing what was supposed to go to the hardware. You
can check this using debug to write and read from the port. I've
got a page below that tells how to write bytes to the parallel
port pins under XP.

http://www.geocities.com/zoomkat/ppswitcher.htm

 

[Rick Merrill]

Unless you have gotten user level access to the parallel port
hardware, you probably aren't really controlling the hardware.
You are just seeing what was supposed to go to the hardware. You
can check this using debug to write and read from the port. I've
got a page below that tells how to write bytes to the parallel
port pins under XP.

http://www.geocities.com/zoomkat/ppswitcher.htm

thank you thank you !

 

[Rick Merrill]

Unless you have gotten user level access to the parallel port
hardware, you probably aren't really controlling the hardware.
You are just seeing what was supposed to go to the hardware. You
can check this using debug to write and read from the port. I've
got a page below that tells how to write bytes to the parallel
port pins under XP.

http://www.geocities.com/zoomkat/ppswitcher.htm

Using DEBUG I see the same phenom: first out/in
reads what was sent. Next ones do not.

-O 378 AA
-I 378
AA
-O 378 01
-I 378
AA
-I 378
AA

This is unexpected! - RM

 

[Si Ballenger]

Using DEBUG I see the same phenom: first out/in
reads what was sent. Next ones do not.

-O 378 AA
-I 378
AA
-O 378 01
-I 378
AA
-I 378
AA

This is unexpected! - RM

You don't have user level access to the hardware, so you aren't
actually changing the pin values. You can use a program called
userport (search google for userport.zip or go to my link above)
to set the registry to allow you to directly control the parallel
port pins on NT/2K/XP. Run userport on your machine, then try the
debug routine again.