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Need help from the old farts! :D How were dense DIP boards routed way back then?

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MarkS:
I'm working on several projects based on the MC68000. To make my life easier (HA!) I am separating everything into multiple development boards. To keep with the retro look and feel, I'm using as close to 100% DIP packages as possible.


Right now I'm working on the processor board. I have all of the buses broken out to female headers via 74LVC245's. No matter how I orient the processor or transceivers, the ratsnest is just a total twisted mess. And I'm giving quite a bit of space between components! Some of the truly densely populated boards of old have chips so close you'd think the pins would short out! I've tried rotating and moving the transceivers and CPU, but all that does is move the twisted mess.


How do I tackle this? I'm going 4 layers, just because of this issue, but in reality, 2 layers should suffice. I can reorder the nets so that they line up better with the transceivers coming from the CPU, only that twists them between the transceivers and headers. I could make the bus out of order at the headers, but that complicates development and ensures nasty errors when wiring between development boards.


How was this done efficiently back in the day?

mariush:
Seems simple to me : U5 to U11 have to be rotated 90 degrees.   Align them as close as possible to the top headers so you more or less have traces go directly from DIP chips to the headers.

You can route some traces UNDER (inside the footprint of ) the microprocessor and some traces can go on the bottom layer of the pcb.  Especially where a bunch of traces have to be flipped/reversed ... use vias to route them to other layer and then you no longer have to reverse them.

If you're reluctant to use VIAs you can use 0 ohm resistors / jumper links to jump over traces where needed.

If the order of the headers is not critical, maybe they can be rearranged to work better, for example CONTROL BUS and the one to the left and U5 and U8 may be better all the way to the right.

jonpaul:
narrow down your pads, route traces in between two pads

j

MarkS:
Thank you! That got me in the right direction!

Terry Bites:
Manual routing is efficent if you have the skills!
Mariush is right.
Placement is everything. Rotate the 245s
Make the pads 64 thou or less. You'll get a 16 thou track through the pin spacing with ease.
Mil to you.
68000 thats old fart territory alright!

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