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What explains the unintuitive numbering of chip pins?
- pwg 6y agoAlso, when creating wire wrap circuits (https://en.wikipedia.org/wiki/Wire_wrap https://en.wikipedia.org/wiki/Wire_wrap) one works from the underside of the board, so the underside pin numbering image shown in the webpage is the pin numbering one follows while wire wrapping a circuit.
- amelius 6y agoWell, we now have packages where pins are on 4 sides (not just 2 sides). For example [1]. So here it certainly makes sense that numbering goes around the package instead of in columns/rows. [1] https://en.wikipedia.org/wiki/Quad_Flat_Package https://en.wikipedia.org/wiki/Quad_Flat_Package
- bnegreve 6y ago> Why are pins counter-intuitively numbered in a rotating fashion rather than by columns as one would expect for a rectangular package? I am not sure why this is counter intuitive, on a 8 pin package, it makes sense to keep pin 5 close to pin 4 to simplify the layout of the wires, and in general, it makes sense to keep consecutive pins close to one another. This applies to vacuum tubes as well.
- thedufer 6y agoIs there something particularly five-y about pin 5? Surely if you called it 8 nothing else would change. No one is suggesting redesigning the whole thing. Just move a few labels.
- krapht 6y agoWhen I look at pin 5 on a schematic, it makes it easier to find on a PCB if it is physically close to pin 4 and 6. This is true in programming too. Spatially close data should be stored in memory adjacent to each other.
- thedufer 6y agoI am definitely open to the idea that the current labeling is actually more intuitive, but note that this is not at all the argument I replied to.
- bnegreve 6y agoYes, consecutive pins are often related in some way. Let say pin 3,4,5 and 6 belong to the same port, and must be connected to a connector on the other side of the PCB. If pins were numbered by columns, you would have to connect two tracks to one end of the chip and two other tracks to the other end of the chip. Once you've done that, routing the remaining tracks is basically impossible on a single PCB layer.
- bnegreve 6y agoIn other words, the standard numbering has the nice property that two pins with a consecutive id number are always relatively close to eachother (whatever the package).
- thedufer 6y ago> If pins were numbered by columns, you would have to connect two tracks to one end of the chip and two other tracks to the other end of the chip. You have missed my point entirely. All you have to do is re-label them. There is absolutely no re-wiring or re-routing implied by changing the pin numbers.
- bnegreve 6y agoNo I haven't, but I've failed to convince you, it seems. It does make a difference because the chip designer doesn't know or doesn't care how the chip is going to be packaged and where the pins are going to be placed on the package. With the standard numbering, two consecutive pins are always placed next to eachother no matter the package, and the chip designer can use this information to optimize the placement of related pins. This is not true with the alternative numbering "by column", where pin 4 and 5 are close on most packages, but far away on a DIP 8 package.
- dboreham 6y agoI think this is wrong. Pins really pads that are numbered on the die. The die is square (or was back then). Pads are numbered in sequence around the pad ring. So the concept of columns doesn't exist in the context of the die. As to why number counterclockwise vs clockwise, possibly that's to do with existing convention from valves. However note that in the beginning dual inline packaging wasn't the norm. There were flip chip packages, die on board, circular TO-xx metal can packages etc. So whatever led to the counterclockwise numbering convention certainly predated DIL packages.
- Waterluvian 6y agoThat's a really good point. So if you wanted a single numbering system for 4-sided and 2-sided chips, the current approach is quite a sensible compromise. If you have the little key symbol in a corner, you can just "walk the chip" from there, regardless of sidedness
- cycomanic 6y agoAlso column wise counting would be a recipe for disaster. It's way to easy to "slip" by a column/row if you move across the chip, so everyone would still be counting up and down the sides just maybe in steps of 2. Might as well do it right then
- phkahler 6y ago
- smoyer 6y agoWhy would a convention be considered unintuitive? You learn it and it's just a design fact. I'm not sure I agree with the article - it seems like a case of human-pattern matching.
- aendruk 6y agoWhat's unintuitive is that it doesn't follow other conventions that could reasonably be applied.
- eqvinox 6y agoWhich conventions would that be?
- aendruk 6y agoReasonable candidates, per the article: - https://en.wikipedia.org/wiki/Left_to_right https://en.wikipedia.org/wiki/Left_to_right - https://en.wikipedia.org/wiki/Clockwise https://en.wikipedia.org/wiki/Clockwise
- eqvinox 6y agoBy that logic: - https://en.wikipedia.org/wiki/Counterclockwise https://en.wikipedia.org/wiki/Counterclockwise Also, it's clockwise when viewed from what used to be the wiring side, i.e. bottom. Also-also, mathematical/engineering sense of rotation for positive angles is counterclockwise. ("The mathematician works against the clock.") Also-also-also, you've listed 2 conventions with no preference between them. If either would have been picked, we would be having the same discussion right now on why it wasn't the other one. The only thing that would give any advantage here is if there were established context or logic giving significant preference to any of them.
- aendruk 6y agoYes, you understand correctly. In this case, assume the life and cultural context of the author.
- deleted 6y ago[deleted]
- emilfihlman 6y agoIt seems like the author just wanted to write about something, and he chose something he's not familiar with but what appears as quirky to him. I expected the article to talk about IC design and peripherals (the placement of which is what is actually something that might seem unintuitive at first to many, well perhaps more annoying than unintuitive).
- joezydeco 6y agoIt seems like the author just wanted to write about something, and he chose something he's not familiar with but what appears as quirky to him. Welcome to Hacker News, you must be new here. =)
- eqvinox 6y agoThe only pin numbering I ever perceived as unintuitive is on PLCC packages where pin 1 is in the middle of one of the 4 sides. Especially since there's still a marker dot in one of the corners generally. Luckily, PLCCs are rare these days. Example: https://www.zilog.com/manage_directlink.php?filepath=docs/z80/ps0180&extn=.pdf https://www.zilog.com/manage_directlink.php?filepath=docs/z8... (Note that the orientation on the PLCC package is indicated by one of the corners being different, yet that's not where pin 1 is.)
- neltnerb 6y agoYeah, I've seen those. Do you have any idea why they did that? I had twenty or thirty on a recent board and they took so much extra work to double check because they didn't follow convention. I probably read that pinout in disbelief for an hour before I called them to check. I think that's why people number them the counterclockwise way, if they didn't they'd get furious engineers calling them and yelling (I didn't yell, I was just very confused) that they aren't following the standard. There are so many ways to make a mistake in a circuit board already, once someone decided on a numbering scheme momentum probably just kept it going to be honest. Why would you change it when there is no functional difference and it makes mistakes less likely?
- eqvinox 6y ago> Do you have any idea why they did that? No, not the slightest clue. If you find an answer, I'm interested too...
- neltnerb 6y agoAll I can find is the definition, which states that pin one is in the middle of the top at least in the 44 pin package. http://www.interfacebus.com/ic-package-plcc-dimension-outline-drawing.html http://www.interfacebus.com/ic-package-plcc-dimension-outlin... No idea on the history though, hopefully someone can enlighten us, Google did not.