Re: VDU question

[Wayne Warthen <wwar...@gmail.com>]

Hi Oscar,

Well, I will just make a couple comments.  

First, The VDU driver code in RomWBW is almost purely the original code that I found in a previous ROM.  I really did not change it.

Second, I will add that I have built the board and am running it under RomWBW.  I found that on some monitors I have the top line cutoff and on some I do not.  I assume there is a display timing issue, but have not looked into it any further.

-Wayne

On Thursday, September 27, 2012 1:58:41 AM UTC-7, oscarv wrote:

Hi all,

I recently completed a whole set of N8VEM boards (VDU, Zilog Peripherals, Disk IO and the 6809 board) to expand my N8VEM.

I have one question on the VDU... this is quite an old board by now so I wonder if anyone still has answers!

The board works well with RomWBW 2.1 but the top line of the screen is always garbled. See the picture: the top line should just show 'dir'. Also, there is faint but unusual 'ghosting' below the 25th line (second picture).

 

 

 

 

I've read in the old postings that the 6545 CRT chip sometimes needs tweaking of screen parameters, but I doubt that is the problem here - I get the exact same picture on two monitors. Both are PAL monitors but both are supposed to be able to deal with NTSC (I don't think that is where I should look for a solution). One monitor actually developed a scary crackling noise after 10 minutes - but that may be unrelated, as it hasn't been used for more than an hour in this century.

I'm not sure where to start my bug hunt - any suggestions are very welcome!

Regards,

Oscar.