[Coco] Selling my 512k Coco-3 and related items

[Dave Philipsen]

I know nothing of the circuit being mentioned here but I can relate a couple of facts that I know. If the monitor is in requirement of a composite sync signals (as some do), and the sync signals are both negative and they are both coming from open collector outputs or TTL type outputs with pull-ups you can tie them together to create a composite sync signal. TTL negative logic signals can be tied together to logically OR them without even using a gate. Some older monitors I have seen use composite sync as a separate signal and others I have seen combine the composite sync with the green video signal. 

Dave

> On Dec 7, 2018, at 5:45 PM, Bill Gunshannon <bill.gunshannon at hotmail.com> wrote:
> 
> 
>> On 12/7/18 4:54 PM, Stephen Fischer wrote:
>> Tie Sync together??????
> 
> 
> That's what I thought, too.  But the picture states that he has HS and 
> VS tied
> 
> together run through a resistor connected to the Sync line of an RGBS 
> connection.
> 
> He has pictures that seem to show it working, but I don't  know how.
> 
> 
>> 
>> The only way is to use an NOR chip, 74??00 if I remember the number 
>> correctly. Then if needed to invert the polarity another NOR gate is 
>> available on the IC.
> 
> 
> He has an example of such a combiner but claims he didn't need the
> 
> complexity and just used the cable.
> 
> 
> I admit to being baffled.
> 
> 
> bill
> 
> 
> 
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