ELEC 332

In the Lab III: I2C DAC Card

You should now have everything you need to assemble and test the I2C DAC card: the components, the PCB, and the software. At this point, everything that needs to be done is stuff we've done before, so this exercise should be over in no time.

Part 1: Assemble the Board

When assembling the board, don't install the 10 kΩ pullup resistors. They will be added later.

Part 2: Test the Board



Connect the components.

 This will be the same configuration as in Part 1 of the first In the Lab section, except that your DAC board will take the place of the RS232 module.

Build and load the program.

 Fire up the IAR Embedded Workbench, load the lab3 workspace, and select the i2c1 project. Build and download the program.

Try it out.

 Connect the scope to the SMB connector on your board. Start the program. If all is well, you should see a sawtooth waveform on the scope.

Examine the I2C bus signals.

 Using the 10x probe on the scope, look at the signals on the SCL and SDA lines and estimate their rise times.

Install external pullups.

 The I2C specification calls for external pullup resistors. In the interest of economy, and because we're running the LTC1669 from a 5 volt supply (another cost saving design choice), we have been utilizing the MSP430's internal pullups. Although these are weaker than the spec suggests, we can get away with it because our connection path is short. To see what difference the use of external pullups makes, install them now and repeat the measurements of the previous step.