Board layout question...

[cbmeeks]

I'm laying out my board (PCB) and I'm putting the pads in for pull-up resistors.

It's going to be a tight squeeze to get each one next to the 65C02 pins.

So my question is, how close should pull-up/down resistors be to their respective pins?
Obviously, as close as possible but if I have a small area...say 2-3 inches away...that could hold a group of resistors nicely, would that be an issue?

Max speed of this board would be in the 1-4 MHz range.

Thanks!

[BigDumbDinosaur]

cbmeeks wrote:

I'm laying out my board (PCB) and I'm putting the pads in for pull-up resistors.

It's going to be a tight squeeze to get each one next to the 65C02 pins.

So my question is, how close should pull-up/down resistors be to their respective pins?
Obviously, as close as possible but if I have a small area...say 2-3 inches away...that could hold a group of resistors nicely, would that be an issue?

Max speed of this board would be in the 1-4 MHz range.

Thanks!

At the speeds you're are contemplating distance shouldn't be critical.

I used a SIP for the pull-up resistors, rather than individual resistors, since most of them are connected to MPU pins. I was able to tuck the SIP in real close to the MPU's socket.

[GARTHWILSON]

cbmeeks wrote:

So my question is, how close should pull-up/down resistors be to their respective pins?

Since the resistance is going to be far more than the inductive reactance at the highest speeds of interest (say, ~50MHz for the needed harmonics to get a squarish wave at 4MHz), the length of those connections won't have any significant impact. If they were super long, reflections could become a factor, but that's not going to happen with the maximum lengths you're likely to have on a reasonable-sized board. I wouldn't worry about it.

[cbmeeks]

Thanks for the information!

@BDD

How did the SIP work? Was it tricky routing all of the input pins to the SIP since it was so close to the MPU?

Thanks

[BigDumbDinosaur]

cbmeeks wrote:

How did the SIP work? Was it tricky routing all of the input pins to the SIP since it was so close to the MPU?

Routing was no problem. As one picture is worth lots of words, here's a pic of POC V2's PCB, with the SIP resistor array pointed out (right side).

POC V2 SIP Resistor Positioning

The particular array I used is a Bourns 4609X-101-332LF, which is eight 3.3K resistors. See attached data sheet

4600x_array_bourns.pdf

Bourns 4600 Series Resistor Array

(235.46 KiB) Downloaded 108 times

[cbscpe]

I had the same problem. But then after some layout sessions I decided to use SMD for all resistors and capacitors. First you don't have holes that occupy space on both sides and second they are really small. To make it not too difficult I'm using the 0805 form factor. Very easy to solder even with a old soldering iron. The one important thing using SMD is that you must solder the parts going from the smallest upwards, else it can be that sockets etc. block the space where you would need to put the soldering iron. However I put the SMD parts mostly on the bottom side, so you can use the space between the pin rows of a IC and you don't have other parts in the way. And last but not least, SMD is much cheaper (a set with 50 values and 100 pieces each together with the box is less than 50USD)