Jasper wrote:
>I've had several reactions on the mail about my broken MSX (Thank you all
>who reacted). But I haven't had a reaction that explaines all of the
>problems. So I will discuss the reaction and my opion on them...
>
>The first thing I heard was a broken VRAM chip. But if one of those is
>really broken, I can't understand the problem the computer has. I thought
>the screen with the MSX logo is screen 5, but please correct me if it
>isn't. To get the problems described, the screen must be stored in two
VRAM
>chips of which one is broken. That means the first pixel (4 bits) goes to
>chip 1, the second to chip 2, the third to chip 1 etc.
AFAIK, the sartup logo is in SCREEN 7, but the point is the same...
This is correct. But mind: the VRAM is built up from bytes, not from pixels
and in SCREEN 5, 2 pixels make up a byte...
>Let's suppose one of those is broken, then the screen will show vertical
>black lines. And because the screen is showing them, it is easy to think
>this is the problem. But now something I don't understand. Why is the
>screen crapped in screen 0? If it is stored in a broken VRAM chip it
>schould be completely black, if it is stored in a working VRAM chip it
>would be ok and if it is stored in two VRAM chips as described before it
>would be partially readable, but even that is not true.
SCREEN 0 is built up differently from SCREEN 5. SCREEN 0 consists of
a screen table, in which all 'ASCII' bytes apper. These bytes serve as
indices in the pattern table, which defines the pixel patterns per
ASCII character. A blown up VRAM chip will result in a corrupt screen table
with indeices to a corrupted pattern table.
Rubbish on the screen is the result. (Hope this is enough explanation -
mail me, if not).
Still, this does not explain the strange reaction on the non-BASIC
programs,
nor the disk problems. My guess is that the 'puter 's had a heavy blow
either electrically, blowing up a couple of IC's, or physically (being
dropped of the 45th floor ;-)), damaging the circuits and leads...
Suc6,
Eric.
