I'm working on a project that requires the use of an Oriental Motor closed-loop stepper-driver package (they're a marvel) and, looking at page 5 of the connection-operation manual, there's a footnote that says:

"Connect a termination resistor of 100 Ω or more between the driver and the input of the line receiver."

What gives? I don't understand what it means. What's the "input of the line receiver"? Are they talking about the R0 shown in pins 9 through 20 to limit the current flowing through the internal optoisolators to 10 mA?

 

The only line receivers I see are on pins (3,4), (5,6), and (7,8) where it says in the picture 26LS31 or equivalent. That part was an actual Differential Line Driver. The companion part was a 26LS32 Differential Line Receiver. I don't know if that sentence is referring to the optos or not. I kinda doubt it because a termination resistor goes across a differential pair.

The actual quote is
"Connect a terminal resistor of 100 Ω or more between the input of the line receiver terminals"

 

The only line receivers I see are on pins (3,4), (5,6), and (7,8) where it says in the picture 26LS31 or equivalent. That part was an actual Differential Line Driver. The companion part was a 26LS32 Differential Line Receiver. I don't know if that sentence is referring to the optos or not. I kinda doubt it because a termination resistor goes across a differential pair.

The actual quote is
"Connect a terminal resistor of 100 Ω or more between the input of the line receiver terminals"

Thanks for clarifying, I copied that quote from a more extensive User's Manual, but then decided to post the connection-operation manual instead, since it's far shorter. But the aforementioned quote is present in both documents, although in slightly different form.
And you're right... I've also always understood a "termination resistor" as being placed across the wires of a differential driver, such as an RS485.
It also seems that the pairs (31,32) and (35,36) are connected from the controller in a differential mode, as shown in the "When pulse input is of line driver type" figure... but maybe this makes no difference, since I plan to use the connection shown in the figure titled "When pulse input is of 5 VDC type" anyway...
thanks for your help!

 

I would have written that footnote a bit differently. It sounds like a translation into English from some other language.
I'm glad to be helpful, but my eyes are getting too poor to read the fine print. It might be a good thing that I'm now retired.
Good luck with your project.

 

... It sounds like a translation into English from some other language...

Now that you mention it, yes, the product is Japanese. If it's a translation issue then I'm a bit disappointed, the Japanese are known for their perfectionism, among other things.
I would've expected a mistake like this from a Chinese product instead.
Thanks again!

 

"Connect a terminal resistor of 100 Ω or more between the input of the line receiver terminals"

My correction would be:

Connect a termination resistor of 100 Ω or more between the input terminals of the line receiver.

Putting a prepositional phrase between the noun and a modifier sounds exceedingly weird. I'll bet it sounds unnatural in Spanish as well.

 

The line upper than the line you mentioned:
Use output signals at 30 VDC or less. If the current exceeds 10 mA, connect an external resistor R0.

 

"Connect a terminal resistor of 100 Ω or more between the input of the line receiver terminals"

My correction would be:

Connect a termination resistor of 100 Ω or more between the input terminals of the line receiver.

Putting a prepositional phrase between the noun and a modifier sounds exceedingly weird. I'll bet it sounds unnatural in Spanish as well.

Yeah, in Spanish it would sound weird too.
My guess is that the termination resistor is recommended to minimize the possibility of spurious triggering while the differntial signal is at 0V due to EMI or some other reason. Am I right?

 

, the Japanese are known for their perfectionism, among other things.
I would've expected a mistake like this from a Chinese product instead.

You may not have said this if you had to contend with the first CNC systems Fanuc imported to N.A. All manuals written in 'Jinglish' . Took three or four readings to decipher!
Max.

 

You may not have said this if you had to contend with the first CNC systems Fanuc imported to N.A. All manuals written in 'Jinglish' . Took three or four readings to decipher!
Max.

You're right, my observation was a little unfair. Everyone has to start somewhere. The Chinese are not perfectionists... yet... but they're getting there... which worries me a little..

 

Yeah, in Spanish it would sound weird too.
My guess is that the termination resistor is recommended to minimize the possibility of spurious triggering while the differntial signal is at 0V due to EMI or some other reason. Am I right?

There are at least two reasons for termination resistors on differential inputs.

1. To keep the differential input at 0V when there is no driving source
2. To provide a current return path for the differential driver

 

Yeah, in Spanish it would sound weird too.
My guess is that the termination resistor is recommended to minimize the possibility of spurious triggering while the differntial signal is at 0V due to EMI or some other reason. Am I right?

I think that(R0) is used to protect the LED of left optocoupler, you can see from the loop of circuit, and the others as EMI that you can also see it in the circuit.

 

There are at least two reasons for termination resistors on differential inputs.

1. To keep the differential input at 0V when there is no driving source
2. To provide a current return path for the differential driver

The first one I understand. But does the second one mean that without the resistor the differential driver wouldn't work? Or is it there to provide a minimum amount of current necessary for the driver to work properly?

 

Argh! @ScottWang .. it seems that I accidentally edited my last post, instead of answering yours, and garbled its meaning. Can you, as a moderator, put it back the way it was?

 

Argh! @ScottWang .. it seems that I accidentally edited my last post, instead of answering yours, and garbled its meaning. Can you, as a moderator, put it back the way it was?

I'm not sure what you want me to do and what back to where in post #13?
I saw you said the "across", but I can't find the word in the datasheet, the across means that they are in parallel, the one component in parallel with another component, does that just you thought that or you see it in the datasheet?

 

I'm not sure what you want me to do and what back to where in post #13?
I saw you said the "across", but I can't find the word in the datasheet, the across means that they are in parallel, the one component in parallel with another component, does that just you thought that or you see it in the datasheet?

Thanks, Scott. But never mind. I've re-edited post #13 to its originally intended form.

 

The first one I understand. But does the second one mean that without the resistor the differential driver wouldn't work? Or is it there to provide a minimum amount of current necessary for the driver to work properly?

Think about what happens if there is no current return path. A differential signal comes down the line and takes the high impedance input to some levels. Now the driver signal goes away and the transmission line now has a charge on it which must be dissipated. If there is no return path to the source it might just stay there. After the charge on the cable is discharged the termination resistor makes sure the inputs have 0 V differential on them.

 

Now that you mention it, yes, the product is Japanese. If it's a translation issue then I'm a bit disappointed, the Japanese are known for their perfectionism, among other things.
I would've expected a mistake like this from a Chinese product instead.
Thanks again!

Have you worked for a Japanese company? Conversational English translations were good but technical translations were a nightmare. We hired in-house translators to read the original texts and had a few Japanese-American engineers who were still baffled on how to say the English equivalent. I hear that today most of the translations are not done in Japan so you have a three language tower of babel with sometimes funny results.

Warning NSFW but funny.

https://www.youtube.com/watch?v=e6-B2TJN8UQ

 

Think about what happens if there is no current return path. A differential signal comes down the line and takes the high impedance input to some levels. Now the driver signal goes away and the transmission line now has a charge on it which must be dissipated. If there is no return path to the source it might just stay there. After the charge on the cable is discharged the termination resistor makes sure the inputs have 0 V differential on them.

Ah... I think I get it now... the differntial receiver works through interpreting voltage but has no capability of sinking current all by itself... that's the second reason why the termination resistor is there. Right?

 

Ah... I think I get it now... the differntial receiver works through interpreting voltage but has no capability of sinking current all by itself... that's the second reason why the termination resistor is there. Right?

I think so.