I2C port IO chips

You could roll your own out of an AVR or PIC. Plenty of I2C examples out there.

Peter

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Have you checked usual distributors? I don't know where you are but places like Farnell sell them.

Andy

Beside that it can be done with IO ports in PICs and AVRs, it could also be done with a small CPLD.

Rene

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I2C is patented/copyrighted/trademarked. Look for '2-wire interface' parts, maybe.

TI second source the PCF8574.

They also seem to have dropped their prices....

Maxim have a range of IO exanders, with SPI and i2c versions. There are also SMbus devices, and SMbus is a PC variant of i2c. Unlike i2c masters, Slave i2c devices generally need some HW support - take a look at the Cygnal uC & Philips LPC9xx families, as most of these have i2c HW support, and many of the smaller uC these days price compare reasonably with the dedicated i2c IO options.

-jg

Sell what, Philips chips? I am in the US. I believe Farnell is Australia, right?

I could go to a lot of different distributors, but other than Philips, I don't know of any parts. All the distis I have checked only sell Philips parts in large quantities. I guess I could ask for a few dozen samples. So far Arrow is being very obliging. They sent me a couple hundred $.25 capacitors.

No, Europe.

Try the US-counterpart of Farnell: Digikey.

Do a search for the PCF8574AN and you'll find they have 415 in stock and sell for $2.00 a piece.

Meindert

maybe.

Is '2-wire interface' always actually I2C, if avoiding the trademark issue?

I see a lot of SPI devices around - Would I be right in thinking that SPI is faster than I2C? Is it *better*?

ABS

Hi, spi is harder to get multi master bus to work than i2c. I2c goes up to at least 400khz.

Ralph Malph schrieb:

As already mentioned, PCF8574 should be available in distribution. (At least here in Europe, it is, in rather small quantities, and even at hobby-electronic vendors.)

I2C is slower than other serial interfaces, but the advantages are multi-master and fewest wires. If you need cheap and rather fast I/O expansion, and have a few more wires, try using simple shift registers ('165 for input, '595 for output) - you can cascade them easily, and often you can share some signals with other peripherals.

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maybe.

I'm hesitant to say "yes". It's not officially I2C unless it's logo'd. Really, you have to look at the datasheet for the part. If you are bit-banging, it doesn't make much difference, does it?

SPI is different. I2C is great for addressing "registered" components scattered around a board without introducing large PCB routing problems. By "registered" I mean, devices that contain a few control registers but don't handle constant bulk transfers. For example, an I2C-controlled digital pot controlling the contrast voltage on an LCD. You set it occasionally.

SPI is more efficient for "streaming" devices such as audio codecs, where there is a small amount of setup and then the device spends most of its life sinking or sourcing a constant stream of data.

SPI is also somewhat easier to work with from a bit-banger's perspective. And it's easy to isolate; you can also keep dead peripherals off-bus with a simple switch controlled by the device's select line (whereas in I2C you either need an intelligent buffer chip in between slave and bus, or you need to rely on the slave's port working right).

The above comments are of course at least partly subjective.

Ralph Malph napisal(a):

Use 596 for outputs. Thet are much cheaper, easier to buy and their footprint is smaller.

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- I'm an engineer.

maybe.

Ah, but I don't plan on bit-banging :-) There's a hardware I2C interface in the LPC2106, for example, and it also matters if one is wishing to have multiple devices on the same bus.

Perhaps "interoperable with I2C devices" is a better wording ;-)

I've noticed the protocol does seem to let a master keep control of the bus for an arbitrary number of bytes - is that the root of the difference you're referring to? Plus the chip select thing means that there's no addressing overhead. At the cost of more traces on the board and more I/O pins used, even if you use a 3-8 or 4-16 decoder :-/

I've looked at CAN, as well. I see uPs with CAN interfaces built in, and CAN interface chips that are external to uPs. I get the impression it's mainly used to communicate between uPs rather than as a uP -> device control bus.

What I would *love* *love* *love* to see is a big directory of I2C, "2-wire", SPI, and (if they exist) CAN peripherals, all on one site if possible, so I can really compare what's available. My favourite semiconductor catalogues organise ICs by function rather than interface, making it awkward to really build up a picture of what's available in my head. Philip's site has a listing of all their I2C devices, which is a start, though.

Like so much in life - but thanks for satisfying my curiousities :-)

ABS

Thanks for your post, and all the others as well. Once I was clued into the fact that I should be searching for "SMB" and "2wire interface", I found several other companies that make I2C stuff (or SMB which is nearly identical).

I originally wanted to use shift registers. But I need something that does not flop the outputs around as you are shifting in as well as being

5 volt tolerant and very small. The 74xx594 would be perfect, but it is not being made in the newer technologies. I prefer the QFN package and not many parts are currently available in that yet. In fact, I found that although TI and Philips second source each other and both have QFN packaging for their logic, they use *different* QFN packages. I can't think of why TI is using a larger width for their package. In fact one of the data sheets I had showed a 2.5 mm QFN, but all the other references TI has show the 3.5 mm package. If it is not second sourced, I am much less likely to use it.

So there are many sources for I2C IO port chips. I think I can even find some that meet all my requirements and are second sourced which makes life so much easier. The fact that I can get many of them from sources like Digikey is the icing on the cake for doing the prototypes.

:)

I think you are referring to the 74xx596. This chip would be good except for two things. 1) it does not have a clear on the output register, and 2) it is only availble as an LS part. I don't want to use technology that is that old and a 5 volt part is not compatible with much else on the board.

But then in a long search, I found the TPIC6B596 which is very interesting. But the smallest package is a 20 pin SO. The price is right, $.56 @ 1000.

OnSemi make a JLC1562, which is essentially pin compatible with the

8574, and adds a 6 bit DAC. Beware though that the SMD part is 0.2" wide, and the 8574 is 0.3" wide.

btw we will have a couple of simple PCBS that take 8574 / 1562's available in a week or so..

Simon

I think we have a few hundred PCF8574's on the shelf available at less than commercial prices. Contact me directly for details.

Also search for 'SMD' as 'IIC' is copyrighted by Philips. We've made I2C peripherials out of Atmel parts in the past which permits smart peripherials but limits the bus speed to about 65khz instead of the

100/400khz.

-- Regards, Albert

---------------------------------------------------------------------- AM Research, Inc. The Embedded Systems Experts

916.780.7623

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On may make good parts, but they have the worst web site I have seen other than the Asian companies. I did a search on "I2C Bus I/O Expander" and came up with >700 hits. There is no way to further filter or do an advance search. All I can do is try to come up with more keywords, which I actually think would give me *more* hits since they seem to be doing an OR rather than an AND of the words.

How can smart people like ON semi be so dumb?