Electronics > Projects, Designs, and Technical Stuff
How to even start routing this?
Joanna_H:
Thanks for all the replies, wow I have a lot to think about...
Unixon:
1) Make best possible placement. I see whole busses running between ICs from one end to another. This is bad, try putting these ICs with individually wide connections next to each other, so that a lesser number of signals would have to run long distances. Traces eat board space very badly, you can save a lot of it with a good layout. By the end of step (1) it may already become obvious how to route a board, because you will know what places you were trying to make traces run through.
2) First route traces that you're better know how to, do short traces. For long traces route only end segment near IC, not the whole length.
3) Next route traces that you have less good idea of how they should run, and again, start from both ends and join in the middle.
4) Finally, solve routing problem for the few most difficult traces with a lot of side switching and snaking around.
The idea about this approach is that it is much easier to route the board moving along uncertainty gradient: start from places where uncertainty is next to zero and you absolutely sure how things must be, then gradually move to places where you have not a slightest idea of if it even possible to do. The trick is, at the end of this path, not much of a ratsnest will survive the routing. Have fun with it.
Joanna_H:
To answer the other questions, this is a simple SVGA 800x600@60Hz Graphics display. It's a module that I've been putting together to go with a load of other modules I'm creating to make a watch as it works CPU, variable speed up to a max of 1Mhz. The 40Mhz is required due to that being the specification for the video out. 99% of the logic is standard 74 series, when not it's all TTL compatible outputs, all running at 5V.
tautech:
Others might have a different approach but I always start PCB layouts with the schematic sheet on the next monitor and visualize breaking the circuit into functional blocks then to lay the components for each block together in little groups in a way that they might each Autoroute OK. Some things are set in stone like I/O sockets and the like so place and lock them and jiggle around with the remaining.
Then you have each little groups rat nest connections and then select each group in turn and move them around and keep a watch for routing paths to be plainly seen that might allow all the little functional blocks to be linked together. When you get/find a layout that might work Autoroute it and look for what needs improving for signal integrity or whatever.
Lots of Autoroute/UnAutoroute trial and error will find a way that works that can be further tweaked to get a good looking layout.
Good luck and be prepared to put real time in for a good job.
Ice-Tea:
Take the advice of others.. Go to a 4-layer board. If this is a paying job, the extra cost will be offset easily by the saving of labor and the probably saving of a respin because of performance/EMI issues.
Use a calculator from a local (Eurocircuits or somesuch) or an offshore supplier (such as PCBway) and you'll soon figure out in most cases going 2 layers just isn't worth it..
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