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Electronics => Electronics => Topic started by: madsci1016 on October 29, 2009, 09:25:05 PM

Title: Are Two wire Interface and I2C the same thing? This says no.
Post by: madsci1016 on October 29, 2009, 09:25:05 PM

Everywhere i look, says TWI and I2C are the same thing with different names.

Why the does this sensor's

http://www.sparkfun.com/commerce/product_info.php?products_id=8257 (http://www.sparkfun.com/commerce/product_info.php?products_id=8257)

datasheet

http://www.sparkfun.com/datasheets/Sensors/SHT1x_datasheet.pdf (http://www.sparkfun.com/datasheets/Sensors/SHT1x_datasheet.pdf)

say otherwise? "The sensor
cannot be addressed by I2C protocol, however, the sensor
can be connected to an I2C bus without interference with
other devices connected to the bus."


Can anyone clear this up?

Title: Re: Are Two wire Interface and I2C the same thing? This says no.
Post by: chelmi on October 29, 2009, 10:03:16 PM

Unless I'm mistaken the datasheet does not say that it uses a TWI either. It says it uses a 2-wire serial interface, but I think this is a generic term and does not refer to TWI. For instance the PS/2 mouse and keyboard protocol is also a 2-wire serial interface but has nothing to do with I2C and TWI.

Chelmi.

Title: Re: Are Two wire Interface and I2C the same thing? This says no.
Post by: madsci1016 on October 29, 2009, 10:18:40 PM

So you are saying this sensor has it's own proprietary communications method?

While i'm not saying your wrong, how is a sensor that implements a non-standard communications protocol worth anything?

Title: Re: Are Two wire Interface and I2C the same thing? This says no.
Post by: chelmi on October 29, 2009, 10:51:03 PM

After looking at the protocol more carefully, it seems to be "compatible" with I2C, meaning that a I2C capable device might be able to communicate with it "easily". However it does not seem to follow the I2C/TWI standard.

Chelmi.

Title: Re: Are Two wire Interface and I2C the same thing? This says no.
Post by: arixrobotics on October 30, 2009, 06:46:03 AM

I don't really know much about I2C and TWI protocol, so I can't comment much on your issue. However, I'd like to share some probably related info.

1. I read in an article about RTCs, and they said the datasheet for this particular RTC chip does not state that they are using I2C to avoid paying royalties. They just say its a two wire protocol.

2. The DS1302 RTC chip uses a two wire protocol, but not I2C. I had to write some kind of bit banging code to get it to work. So there are some devices which do not implement standard communications protocol.

:-\

Title: Re: Are Two wire Interface and I2C the same thing? This says no.
Post by: GearMotion on October 30, 2009, 07:24:49 AM

Quote from: arixrobotics on October 30, 2009, 06:46:03 AM

2. The DS1302 RTC chip uses a two wire protocol, but not I2C. I had to write some kind of bit banging code to get it to work. So there are some devices which do not implement standard communications protocol.

The DS1302 has a chip select, clock, and bidirectional data line. It isn't two-wire / I2C as the communication delimiters are the selection and deselection of of the chip enable (CE) line, not the signal transition during a high clock like I2C. It is more like SPI with MISO and MOSI lines connected.

Title: Re: Are Two wire Interface and I2C the same thing? This says no.
Post by: madsci1016 on October 30, 2009, 03:45:01 PM

Thanks, I'll start googling, but are there any libraries written for this (that you know of), or am I implementing this from the ground up?

Title: Re: Are Two wire Interface and I2C the same thing? This says no.
Post by: chelmi on October 30, 2009, 05:10:33 PM

look at the application notes from Atmel:

http://atmel.com/dyn/products/app_notes.asp?family_id=607 (http://atmel.com/dyn/products/app_notes.asp?family_id=607)

AVR155 is probably a good start.

Chelmi.

Title: Re: Are Two wire Interface and I2C the same thing? This says no.
Post by: Soeren on October 31, 2009, 12:14:44 AM

Hi,

Quote from: madsci1016 on October 29, 2009, 09:25:05 PM

http://www.sparkfun.com/commerce/product_info.php?products_id=8257 (http://www.sparkfun.com/commerce/product_info.php?products_id=8257)

Please tell me you didn't pay $42 for this?
The company used to give away free samples of that chip, at least about 10 years ago (I still have a couple of them in mint condition, as I simply never got around to including them in a proto - oh well, seems like there's another project in the quieve then :))

Look at: http://www.sensirion.com/en/pdf/product_information/Sample_Code_humidity_sensor_SHTxx.pdf (http://www.sensirion.com/en/pdf/product_information/Sample_Code_humidity_sensor_SHTxx.pdf)

Sample Code: http://www.sensirion.com/en/Installationsprogramme/Sample_Code_C1.zip (http://www.sensirion.com/en/Installationsprogramme/Sample_Code_C1.zip)

More to look through:
http://www.sensirion.com/en/pdf/product_information/CRC_Calculation_Humidity_Sensor_E.pdf (http://www.sensirion.com/en/pdf/product_information/CRC_Calculation_Humidity_Sensor_E.pdf)
http://www.sensirion.com/en/pdf/product_information/AN-humidity-formulae.pdf (http://www.sensirion.com/en/pdf/product_information/AN-humidity-formulae.pdf)
http://www.sensirion.com/en/pdf/product_information/Introduction_to_Relative_Humidity_E.pdf (http://www.sensirion.com/en/pdf/product_information/Introduction_to_Relative_Humidity_E.pdf)

Happy reading :)

Title: Re: Are Two wire Interface and I2C the same thing? This says no.
Post by: madsci1016 on October 31, 2009, 10:03:33 AM

Thanks, I'll look through it when i get a chance.

I Have not paid $42 for those sensors yet, if you know of a better product I am open to suggestions.

At this point i might give up humidity and just use something like this

http://www.sparkfun.com/commerce/product_info.php?products_id=9418 (http://www.sparkfun.com/commerce/product_info.php?products_id=9418)

at $6 and a I2C interface.