Terminating Resistors in Digital Circuits

Thread Starter

PauloConstantino

Joined Jun 23, 2016
266
Hi friends,

I have been building an 8bit CPU/Memory system on breadboards. I know this sound crazy but that's what I am doing...

I have been worried about needing terminating resistors. I am not an EE so my knowledge is limited.

What is the condition for terminating resistors? Where should I put them exactly? And what should be the values?

I greatly appreciate your help.
 

EM Fields

Joined Jun 8, 2016
583
Hi friends,

I have been building an 8bit CPU/Memory system on breadboards. I know this sound crazy but that's what I am doing...

I have been worried about needing terminating resistors. I am not an EE so my knowledge is limited.

What is the condition for terminating resistors? Where should I put them exactly? And what should be the values?

I greatly appreciate your help.
Generally, terminating resistors are Bad Things unless you need to match the impedances of the source, the load, and the transmission line between the soruce and the load, and your loads can take the 6dB hit in amplitude with impunity.

It would be most helpful if you'd post a schematic showing what you're up to and identifying the CPU and the memory elements.
 

DickCappels

Joined Aug 21, 2008
7,297
If it is the 74HC or 74H logic you mentioned in another of your posts, you won't need terminations unless you have some very long signal runs.

You mentioned "breadboards" -I would be much more concerned about signal integrity resulting from the use of plug-in breadboards which cannot give you very solid ground and power supply busses, even with heavy bypassing just because of the series inductance you are likely to have in those paths. You might find the discussion in the application note below to be helpful.

Minimizing Ground Bounce & VCC Sag - Altera
 
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