Re: VDU question

[vk5dg <vk...@internode.on.net>]

Hello Oscar,

I've recently got my VDU card running and have been adding comments to the source code as I discover new things about it.  I can tell you that the firmware is set up for a PAL monitor - it works at 312 lines non-interlaced at 50 fields per second.  Also the jumpers for the character clock must be set as K1 2-3 (pin 3 of the 74669 HI) and K2 1-2 (pin 4 of 74669 LO).  This gives an output of 2 MHz for the CLK signal (pin 21 of the 6545-1).  I'm using a 30 year old green screen monitor on my board and after some adjustment of the picture controls it has given a stable picture.  

Hope this helps for a start.

Regards

David

On Thursday, 27 September 2012 18:28:41 UTC+9:30, 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.