Alternate supplier for dallas/microchip 1-wire memories

For production of measurement probes, we need to store calibration data on them. Because of the limited number of connections, the 1-wire memories look like good candidates. For now we need at least 16kbit of storage which should be eprom or eeprom. The only suitable device from maxim therefore seems to be the DS2505 with 16kbit eprom. (the larger ones are serialized 'uniqueware' devices). In the I-button range are 2 candidates, a 64kbit eprom and a 32kbyte eeprom, but these are rather expensive (but the sealed housing is nice though).

Because of the limited selection and whish for second source, I'm looking for another manufacturer that makes 1-wire memories, but have not found one yet.

Are there any other manufacturers of these devices? Maybe they use different names for the bus as is the case with I2C vs. "Two Wire Interface".

--
Stef    (remove caps, dashes and .invalid from e-mail address to reply by mail)
Reply to
Stef
Loading thread data ...

Microchip has started a range with what they call a UNI/O bus.

Regards Anton Erasmus

Reply to
Anton Erasmus

I've never seen any other sources, but the protocol is simple enough that you can make your own devices using a very tiny MCU. It probably won't be able to be line powered, but it could be lower cost. Some of the Dallas 1-wire parts are not very cheap. But a diode (or an LDO) and capacitor might work to make a low end MCU line powered.

Rick

Reply to
rickman

You are not likely to. It is owned by Maxium. I do not know if they have second sources.

Reply to
Neil

One can even skip the diode - use the internal diode on the pin. Maybe parallel a few pins on a 6 pin PIC could be used to increase the typical 10mA rating for the internal diodes. Just add the cap across the supply. Rocky

Reply to
Rocky

Doesn't that create a possibility of latch-up? Then the MCU would be inactive until the cap drained. I've never actually tried doing this, have you?

Rick

Reply to
rickman

se

bly

of

)

I have tried it inadvertenly. The circuit worked OK, but obviously if is preferable to have all the VDD pins wired !

IIRC the latchup current is in the order of hundreds of mA. The rated current into a pin is 20mA on the 16F88x range. (Checked the data sheet.) One could put a 220 ohm resistor in series which would keep the current limited, but I imaging it would be more to limit the drive current from the main microcontroller than to protect the '1 wire' unit.

Also, by the time the voltage got to a level to support latchup the current would have dropped significantly.

Rocky

Reply to
Rocky

Interesting, but unfortunately completely incompatible with the dallas bus. Also not bus-powered so needs 3 wires instead of 2. But that may be cured as others have written in other replies.

Biggest chip is 16kbit, enough but no future expansion. Other nice feature of the dallas chips is de unique ID, not required, but nice to have.

There also seems to be no second source for UNI/O memories, or does someone know of any?

It looks like the only second-source option would be using I2C, but that requires 4 pins on the connector, or maybe 3 if it can be made bus-powered. Any experiences with I2C and hot swap?

So it looks like I will have: 2-pin connector OR 3-pin connector OR second-source OR roll my own.

--
Stef    (remove caps, dashes and .invalid from e-mail address to reply by mail)
Reply to
Stef

If I can get it line-powered, this would be an interesting option. And with rolling your own, you're not limited to a particular protocol as well. ;-)

--
Stef    (remove caps, dashes and .invalid from e-mail address to reply by mail)
Reply to
Stef

I don't think you will find that I2C is intended for hot-swap. I am not saying it can't be done, I am saying that it has no built-in support. The one-wire interface uses a CRC to verify communications and in general is intended for noisy or intermittent communications and supports hot-swap.

The one-wire spec is a bit tricky to read for timing, but the info is all there. The only real issue in rolling your own is the timing. An MCU will likely be run on an internal RC oscillator and will need to have some margin of stability and accuracy. The timing margins are pretty wide to handle this, so the RC oscillators on many MCUs will be good enough, but you need to pay attention to this detail. Otherwise the protocol is not difficult at all.

I bet you can even beat the Dallas price on many one-wire devices and end up with a smaller footprint as well (other than the cap and the diode).

Rick

Reply to
rickman

We did a schematic once with external I2C through an LTC4303 buffer which is designed for hot-swap I2C applications. The external I2C was dropped befor the actual board was made, so no real experience with this buffer. If we go for I2C, I suspect I will have another look at it.

If we go with the 1-wire, I think well go with the standard parts at first, but having the option of emulating a part is nice. That leaves our option to bigger memories open and solves the single source issue.

--
Stef    (remove caps, dashes and .invalid from e-mail address to reply by mail)
Reply to
Stef

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.