Which function handles copying into the video ram?

[ib@wupperonline.de (Ingo Brueckl)]

Hi,

I have an old DOS programm that runs fine with dosemu, but the output of a
few characters is strange due to some reasons that aren't important to the
problem.

I assume that the program does its video output by copying directly into the
vga graphics memory (text mode), because it is (and always was) very speedy.

What I'd like to do now: If the programs is going to copy some certain
characters with some certain color attribute to the screen, I want to change
the character, e. g. I need to hook into the dosemu function that is called
for 'copying into the video ram'.

Could someone please tell me where I can find this function and what its name
is?

Thank you very much.