Solved

Writing to a different video page

Posted on 1997-03-17
1
336 Views
Last Modified: 2008-03-10
How do I write to page 1, for instance, in text mode using video mode 3 and directly accessing the video memory?
In this mode video memory starts on 0xB800 I guess. But, if I write from this address I'll be writing to page 0 (as set by INT 10, AH=0x05). Documentation says there are four [0-3] available pages in this mode. I switched to page 1 using INT 10 - AH=0x05, but now how do I write to it? Shall I add an offset of 80X25 = 2000?
0
Comment
Question by:pneves
1 Comment
 

Accepted Solution

by:
indian earned 5 total points
ID: 1249728
INT 10 - function 05h actives the page you want to see in the screen not the page you want to write to, so of course you must add an offset (base adress is always B800h), but this is not 2000 but 4000 because each cell is represented by two bytes (ASCII code and ATTRIBUTE).

This is the formula in 80x25 mode:

offset = P * PageSize + Y * 160 + 2 * X + B

where P is the page (0-3).
      B = 0 if you want to write the ASCII code.
        = 1 if you want to write the attribute.
      PageSize = 80 x 25 * 2 = 4000.

0

Featured Post

Industry Leaders: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Preface I don't like visual development tools that are supposed to write a program for me. Even if it is Xcode and I can use Interface Builder. Yes, it is a perfect tool and has helped me a lot, mainly, in the beginning, when my programs were small…
This is a short and sweet, but (hopefully) to the point article. There seems to be some fundamental misunderstanding about the function prototype for the "main" function in C and C++, more specifically what type this function should return. I see so…
The goal of this video is to provide viewers with basic examples to understand how to use strings and some functions related to them in the C programming language.
The goal of this video is to provide viewers with basic examples to understand opening and reading files in the C programming language.

679 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question