Date   : Fri, 24 Mar 2006 23:14:07 +0100
From   : Anders Carlsson <anders.carlsson@...>
Subject: Re: BBC to 1084 revisited

On Fri, 24 Mar 2006, David Hunt wrote:

> Pin       Name    Analog Mode     Digital Mode
> 7         CSYNS   Composite Sync  n/c
> 8         HSYNC   n/c             Horizontal Sync
> 9         VSYNC   n/c             Vertical Sync
>
> It looks to me as if there are no separate syncs available in TTL
> RGB on your Commodore monitor.

Umm.. what I did was to connect the composite sync signal from the BBC
to the horizontal sync input. I expected no picture at all, but got one
that is red and black and fades away. Is it expected behavior if the
monitor only is fed one half of the sync signal and the other is not
connected? What if I connect vertical sync to 0V instead of having it
floating?

I've read about LM1881N being used to split both composite video and
composite sync into separate signals. Is it useable if I for some
reason still would want TTL (i.e ~5V) signals at the other end?

> It is a simple matter to connect up to the analogue RGB instead, a
> couple of small signal diodes in series with the RGB+SYNC signals

Some mention diodes like 1N4148, some mention resistors in the 330 ohm
class. Some mention divider chains like it would be a household item.
I'm fairly good at 6502 programming, but terrible at electronics, so
any advice and perhaps a complete schematic would be appreciated.

Regards

-- 
Anders Carlsson