Easy question regarding AD725 schematic: What to use for logical high?

toodles

Zero's Secretary
Joined
Jul 14, 2005
Posts
157
I have a number of the AD725 chips, wide SOIC -> DIP adapters, and all of the other miscellaneous components on hand, and I am now drawing up how I am going ot lay it all out on the stripboard.

My question is about the logical high at TTL levels needed for the NTSC select, and the 'power on' select at pin 5. Since I only expect to use NTSC, ever, and if the chip has power, it should be on, I need to get a high level signal to these two points. My question is, what is the best way to send that signal? Should I:

1. Just wire it straight to the +5v line.
2. Connect it to the +5v line via a pull up resistor of X ohms?
3. Go through the hassle of adding in an inverter, shorting the input of one inverter gate to GND, and connecting the output of that gate to the two points?

Any suggestions appreciated.
 

MrSporty

n00b
Joined
Oct 8, 2004
Posts
23
It would work if you did it the ghetto way and just wired em straight to the +5v but its not a practice i would recommend you get into the habit of.

Your best way is to use a suitable pull-up resistor between each given point and your +5V supply. A standard 4.7k will do fine.
 

toodles

Zero's Secretary
Joined
Jul 14, 2005
Posts
157
Sorry, I sincerely thought that was everything

Ok, this should be the last one.

Datasheet for the AD725 says:
15 VSYNC Vertical Sync Signal (if using external CSYNC set at > +2 V). TTL Logic Levels.
16 HSYNC Horizontal Sync Signal (or CSYNC signal). TTL Logic Levels.

According to my JAMMA pinout, everything uses CSYNC, so that should go to pin 16. Do I use a resistor to connect pin 15 to +5v in the same way as above?
 
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