Solved

Writing to a different video page

Posted on 1997-03-17
1
333 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

PRTG Network Monitor: Intuitive Network Monitoring

Network Monitoring is essential to ensure that computer systems and network devices are running. Use PRTG to monitor LANs, servers, websites, applications and devices, bandwidth, virtual environments, remote systems, IoT, and many more. PRTG is easy to set up & use.

Question has a verified solution.

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

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…
Examines three attack vectors, specifically, the different types of malware used in malicious attacks, web application attacks, and finally, network based attacks.  Concludes by examining the means of securing and protecting critical systems and inf…
The goal of this video is to provide viewers with basic examples to understand recursion in the C programming language.
Video by: Grant
The goal of this video is to provide viewers with basic examples to understand and use while-loops in the C programming language.

808 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