maxtherabbit wrote:
Yes the inputs are tied together.
You do not need the additional resistor for TTL (or CMOS LVTTL) sync inputs. From the wiki:
Quote:
Every GBS board comes with ~500 kOhm termination on the sync input.
This termination is meant for VGA and most arcade boards. It is unfit for most other sources however.
If you want to use the RGBS input for regular TV level sources (game consoles), the GBS requires one additional 100 Ohm resistor to ground on the sync input.
Together with the factory resistor of ~500 kOhm, this will bring the total termination close to TV levels of 75 Ohm.
(typo in that text - it's actually a 500ohm factory resistor)
Ah, thanks, good to know. Sounds like I could just put a resistor in series onto my adapter's sync line then. I think I would prefer that instead of using an additional termination resistor + needing a switch for when I want to use VGA.
maxtherabbit wrote:
I.e. you only need to add the resistor if your are driving the board with video level sync, which in my opinion shouldn't be done anyway. If you are using a console with native csync output just pipe it directly to the GBS, otherwise use a sync stripper.
Would video level sync be any sort of risk to the board/IC despite its typically lower voltages?
maxtherabbit wrote:
As to whether 5v TTL sync is unsafe for the TV5725 - strictly according to the datasheet the maximum voltage on any input is VDD+0.3V. However, in practice I've driven it with 5V TTL sync and experienced no issues. It's well possible that it would degrade the IC over time doing this, but as cheap as the things are I'm willing to chance it.
The console output dongles I've designed for use with the GBS however are 100% safe to use per spec. They show 3Vpp at the TV5725 input.
rama wrote:
Fixed the wiki:)
And yeah, I'll go with 3.3V level sync being safe, most likely.
If you have 5V levels, consider adding a series resistor (around 470 to 680 Ohm) to protect the sync input.
Excellent, thanks guys. A series resistor is definitely the way I'm going to go for my setup.