Techniques to reverse order of signals on a pcb... - Page 1
Forum section: electronics / projects

author: alank2
author_rank: Super Contributor
timestamp: March 24, 2018, 03:24:23 pm
content: Let's say you have 8 signal lines that are in the order D0-D7, but you need to reverse them to D7-D0. What techniques/elegant ways have you seen that can swap them?Here is what I've come up with (attachment)...

author: amyk
author_rank: Super Contributor
timestamp: March 24, 2018, 04:07:54 pm
content: Hard to come up with a solution without a specific use-case, since I'd usually just rotate the device 180 degrees or move it on the other side of the board...Also worth mentioning that most "dumb" memory devices have no difference between the various data and address lines; they're just labeled that way, and even those whichdohave an order may be able to have it changed in software.

author: Mechatrommer
author_rank: Super Contributor
timestamp: March 24, 2018, 04:09:40 pm
content: reprogram or rearrange the chip so we dont have to do that pcb nasty hack...

author: alank2
author_rank: Super Contributor
timestamp: March 25, 2018, 03:06:02 am
content: I agree that pin swapping is ideal when you have that option. I would have thought there would be some techniques or tricks to this.

author: tautech
author_rank: Super Contributor
timestamp: March 25, 2018, 06:27:31 am
content: Quote from: alank2 on March 25, 2018, 03:06:02 amThere are.Namely component placement in the first instance. Examine what nets as 'set in stone' and which can take other paths to allow better pathways for the final layout.Final routingcanbe the easy bit if you've spend enough time beforehand.Double sided layouts where traces that go to the next device in the signal pathandplaced on the other side of a PCB effectively mirrors the pinout so no reversing of traces is needed.I might use auto-route 10 times on a simple boardjustto get a handle on best orientation and placement before routing manually for the final time.Good layouts take real time. Period.

author: bson
author_rank: Unknown
timestamp: March 25, 2018, 07:41:54 am
content: Go SMD and place one part on each side.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 25, 2018, 07:55:10 am
content: I do it more or less as pictured. If I have the space, I'll go for more symmetry: the vias go along one side, and the traces entering and exiting both make mitered 90 degree bends over to the row of vias. Or if it's a right angle, some space can be saved by placing the vias in a diagonal row and connecting top and bottom layers accordingly (like a keyboard matrix).Best is to follow the buses back to their origins and swap any pairs you can, at the source, or along the way. If you are very tight on space, you can use this method to distribute the space taken up by the swap, along the route.If you have large pads (SOIC or DIP, say), you should be able to get a couple swaps for free, by weaving traces between pads.Ideally, you keep enough space at the row of pins to simply exit that row from the other side, flip the bus around and be done, but sometimes that's not possible.Equivalent-function ICs can help, too. Compare 74HC273 to '573, etc. The former usually sucks more, but, who knows, maybe the quirkiness happens to win for once!Tim

author: bson
author_rank: Unknown
timestamp: March 25, 2018, 09:20:54 pm
content: On a less glib note, like tesla notes one way is to place the components at 90 degrees and use a single 45 degree row of vias, reversing the order as it switches from/to hor/vert.

author: MadTux
author_rank: Frequent Contributor
timestamp: March 25, 2018, 09:29:24 pm
content: (S)RAM (or anything which only the uC writes/reads) usually doesn't care which data line is connected to which data pin.(E)EPROM binaries can be rearranged so that the data fits the PCB layout.Anything else, use 4layer PCB, jumper wires, bridges...... and test it on breadboard, wirewrap board...... before doing the final PCB. Nothing more annoying than spending lots of time designing a PCB that doesn't work