Silly question about pull up resistors on DIN modules

[m00dawg]

I read on uCApps that the pull-up resistors on the serial lines (R33-R36) are for if an IC is not plugged into a socket. I'm using SMD SRs directly on my control surface boards such that I really only need a pull-up on the serial line for the last SR on the board before it goes to the next set of pin headers, correct?

So basically:

J9 In Header -> SR -> ... -> SR ->---+---> J9 Out Header

                                     |  

                                  Resistor

                                     |

                                    +5V

Hopefully that makes sense :) Basically the resistor is before the J9-Out in case there is not another board (and thus another set of SRs) connected to that header.

Edited December 23, 2011 by m00dawg

[TK.]

yes, thats allowed

Best Regards, Thorsten.

[m00dawg]

Awesome, thanks TK! Glad to know my assumption was correct.

[nILS]

I'd still suggest putting it on ther, because you never know it you're gonna extend it some day. Quoting SmashTV:

"Funny, how a two cent part's got you chasing your tail now, right? ;)"

[m00dawg]

I was always going to have it for my output headers. All the stuff on each control surface module will always be populated (wouldn't make sense not to). But, for instance, my last control surface part in my chain (the ENV/OSC section) still has output headers if I wanted to add another module in the chain.

So the question was if I needed resistors for the SRs on the same control surface board. Sounds like it's a no. On the other hand, I already have them laid out and routed on all my boards so it can't hurt to keep them there I don't think. Not having them would give me more room for my ground and power planes though.

[TK.]

We have to differ between a SMD, and a through-hole based solution (especially if IC sockets are used).

It's unlikely that the PCB can still be used if the SMD chips will ever be desoldered. ;)

Best Regards, Thorsten.

[m00dawg]

Yup, but the orientation of the modules could differ. Hence, I should always err on the side of caution and have a pull-up before my out-pins is what the consensus sounds like (or, if in doubt, just put in pull-ups as per the standard DINx4 design :) )