LaunchPad I2C Communication

[iragdoll 0]

Does anyone know how to communicate between LaunchPads using I2C Communication? I would like to have a master unit connected to many slave units. The master unit will most likely be a computer, but I would like to simulate the master as a LaunchPad or Arduino microcontroller. The slave units must all be LaunchPads.

 

Which pins do I use for I2C communication? Any code examples? Do I need pull-up resistors?

 

Any help will be much appreciated!

[bluehash 1,581]

I think I just answered you via the TI-Launchpad group.

 

Quoting it here:

Cde connected a port expander to the Launchpad via I2C

His project is here.

 

Remember to thank him if this works for you

[cde 334]

Yea, the I2C Explorer has a bus-pirate like way of communicating from a pc through the uart to an i2c bus. It uses the builtin USI of the msp430G2231 to handle receiving and transmitting. It is nearly exactly what the TI description of how to use the USI for I2C master shows, put in C code.

MSP430 Family Guide with USI description (PDF Page 449):

http://focus.ti.com/lit/ug/slau144e/slau144e.pdf

 

What you want is USI Slave though. It does not implement that. TI has great USI Slave examples that run on the msp430g line (I have not personally tried them).

 

TI also has a precreated I2C USI code library in assembly, for both master and slave operation, which I would assume is a higher order more optimized than mine

http://focus.ti.com/general/docs/litabs ... r=slaa368a

The pdf explains how it is used, functions and all, while the zip has the actual library.

 

Additionally, you can use a software i2c slave, not using the builtin USI peripheral. Based on a msp430f2131, which has 8kb, so I'm not sure it will run on a valueline part:

http://www.ti.com/sc/docs/psheets/abstr ... laa330.htm

Again, PDF for code examples, and zip for actual code.

I'd go with using the USI instead of bitbanging it. The USI is better, it handles open drain pins, and it can deal with clock stretching.

 

There is also a way to implement a SMBus Master or Slave on the msp430:

http://www.ti.com/litv/pdf/slaa073

SMBus is basically i2c v1.1.

 

Finally, there are full examples that can run on the msp430g valueline chips.

http://www.ti.com/litv/zip/slac080h

It is the MSP430F20xx, MSP430G2xx Code Examples (Rev. H)

The ones you want to look at are (Depending on if you Use C or Assembly) USI 06-16. Show how to implement USI based I2C Masters and Slaves, for single and multi-byte usage. One even shows how to emulate an i2c eeprom.

 

TLDR: Read the Code examples in

http://www.ti.com/litv/zip/slac080h

Or consider using the TI USI i2c Code Library

http://focus.ti.com/general/docs/litabs ... r=slaa368a

[JMLB 24]

Make sure you have a common ground too. My first serial project was not working because I did not have common ground between my 2 chips

[iragdoll 0]

Hey guys,

 

After looking through TI's code for some time, I still cannot come up with a solution. I need help with the coding and if anyone can send me an example on how to send the value "1" when you press the pushbutton connected to P1.3. I can figure out the master part but I just need help with the slave. Please anyone who can help me with this, I am still a beginner with the LaunchPad.

 

Thanks!

[bluehash 1,581]

Do you just want to detect if the pin goes high? or you want to transfer the value 1 from slave to master via I2C

[iragdoll 0]

I want to send the information from slave to master. The master also has to be able to send data to the slave.

[bluehash 1,581]

You will have to do this in steps.

 

1. Are you sure if your master is working correctly? If so, how?. The best way to test this is test it with a standard I2C sensor like a battery gauge or compass.

2. For the slave...did you look through TI's document.

[bluehash 1,581]

The above link has code is assembly. Thisone is in C

[iragdoll 0]

Okay i was just looking through the documentation and sort of understand it. I might come back and ask you some questions regarding it though. Where are the header and source files for it?

 

Thanks!

[bluehash 1,581]

Using the USCI I2C Slave

[iragdoll 0]

For some weird reason, it is not compiling. I added the header file into the include folder under ccsv4, but it says some of the timer functions are undeclared.

[iragdoll 0]

It says that it cannot build the .out file. Can you try the project yourself and see if it works for you? And then you can sort of help me step by step? Sorry that I am a beginner and do not grasp this very quickly...

 

Thanks for Everything!

[bluehash 1,581]

Thats because it is for the MSP430F2618 chip. You need to port it to the one you are using.

 

If you select the above chip when you set up the project, it should compile. What you can do is use the TI code as an example and then build yours. I'm guessing you have the 2231. You will have to understand the code to do this. Copying code will not work.

 

If you don't understand parts of the code, ask us.

[iragdoll 0]

After I specified my device which is the MSP430G2231, it still says that -- "CALBC1_16MHZ is undefined" -- Any ideas?