I have always scavenged electronic components when the opportunity has presented itself. In this case, I scored this resistor network many years ago. I like resistor networks and have used them several times.



I can't, however, find a datasheet for this one - probably because it became obsolete long ago. The 220/330 must be referring to R pairs - right? The black dot is pin 1 - right?

Here is what I read on an MM
1 to 2 or 3 4 or 5 or 6 or 7 - 165.6 Ohms
1 to 8 - 93.4 Ohms
2 or 3 or 4 or 5 or 6 or 7 to 8 - 147.8 Ohms.
All other pin pairs are open.

What is the configuration?

 

Check Bourns for terminator networks. Bourns makes/made many resistor networks and probably something "identical."
I'll have a root around later. I think I have some old CTS data.
I have a vague memory of these being used as TTL terminators for tri-state lines.

 

current CTS part, probably electrically identical: 77085220/330P

 

current CTS part, probably electrically identical: 77085220/330P

*bingo* (I think)

https://www.ctscorp.com/wp-content/uploads/2015/11/770.pdf

Now, I have to spend a head-wrecking hour reading this to try and learn something...after looking at the layout, I am still not automagically seeing how I get those readings from a dual terminated bus...but give me some time...

Thanks.

 

Hello,

This one from bourns has the same configuration:



Bertus

 

Yep, I believe that is it, thanks. In addition to the Vishay appnote in post #4, this one, from Bournes also explains testing and why/how it is used....

The Dual Terminator (or Thevenin equivalent) Network is commonly used for TTL dual-line termination and pulse squaring or ECL line terminations. In ECL line terminator, R2 functions as an emitter pull-down resistor and is normally tied to the most negative supply voltage to provide proper line currents. R1 is normally tied to ground and functions as the termination resistor and in parallel with R2 provides the
characteristic impedance of the transmission line. This results in a zero reflection coefficient of this line to eliminate reflection.

I understand some of this, at least the general idea. I can't say that I will use it anytime soon, but I know more now than yesterday.

 

*bingo* (I think)

https://www.ctscorp.com/wp-content/uploads/2015/11/770.pdf

Now, I have to spend a head-wrecking hour reading this to try and learn something...after looking at the layout, I am still not automagically seeing how I get those readings from a dual terminated bus...but give me some time...

Thanks.

Yeah, I was confused by those numbers too. I thought I understood the math, and I got 91.67 for pin 1-8 on the first try, but it took me several attempts before I got the formulas right for the other two values. Think I understand it now. Let me know if you don't get there and want some help making sense of the readings.

 

I sometimes enjoy trying to create graphic learning tools, so I decided to take a crack at this. The attached PDF goes through the resistor calcs by breaking things down into equivalent resistances, step by step. Hopefully it's helpful.

 

I sometimes enjoy trying to create graphic learning tools, so I decided to take a crack at this. The attached PDF goes through the resistor calcs by breaking things down into equivalent resistances, step by step. Hopefully it's helpful.

Nice.

 

They were common back in the day of TTL. Simple explanation is it sets Vh to 3V rather than 5. This does have the effect of speeding up the High - Low and Low-High transitions.

There are active forms of terminations too.

The pull-up is the simplest.

 

Thevenin Terminations - for those occasions when you don't want to do the dirty work yourself, and International Rectifier has let you down.