MSP-EXP430G2ET: I2C Line staying high after running I2C_standard_master.c sample code

KJ Hobday

Part Number: MSP-EXP430G2ET
Other Parts Discussed in Thread: TMP116, MSP430G2553

Hello,

I have been working with the MSP430 launchpad to send I2C transactions to a TMP116. With no slave on the line I would expect the line to be pulled low then a nack to be received, however when I run the sample master code included in the resource explorer for MSP430, the line stays high the whole time. For reference I had soldered the external pull up resistors and read 3.3V at the SDA and SCL P2.1 and P2.2 pins. I was hoping to better understand the code and why the line possibly isn't being pulled low. See my Saleae log below:

Let me know if you have any additional questions.

4 months ago

0 Dennis Lehman 4 months ago

TI__Guru 64121 points

Hi KJ,

Which MSP430 are you using.

I checked one of the examples (msp430g2xx3_uscib0_i2c_01.c)and it appears to setup P1.6, P1.7 as the I2C pins. Are those the pins you are using?

0 KJ Hobday 4 months ago in reply to Dennis Lehman

TI__Prodigy 250 points

Hey Dennis,

I am using the the MSP430G2553 and the "msp430g2xx3_usci_i2c_standard_master.c" file. For the evm board I had been using P2.1 and P2.2 the SCL and SDA pins with soldered 4.7k resistors for external pull up. I assumed these pins were for I2C use.

0 David Schultz 4 months ago in reply to KJ Hobday

Guru 20595 points

The device data sheet shows which pins do what. Port 2 is pretty much just GPIO and timer functions. Serial port functions appear only on port 1.

+1 Dennis Lehman 4 months ago in reply to David Schultz

TI__Guru 64121 points

Hi KJ,

David is correct. I believe P2.1 and P2.2 is maybe used for a SW I2C (bit-bang) on some of the other MSP430s supported on this EVM.

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MSP-EXP430G2ET: I2C Line staying high after running I2C_standard_master.c sample code