[beagleboard] OMAP Multiplexing on Expansion Header

Hello all,

I am fairly new to the BeagleBoard and I was hoping if someone could answer a couple of questions. I’m trying to connect a couple of devices to the expansion headers. I would appreciate the help.

  1. Are the columns in table 17 from the hardware reference manual mutually exclusive? For my project purposes, I need to be able to utilize 12 lines for GPIO and the two lines for the I2C protocol. In other words, can each pin be independently set up for either option A, B, C or D from table 17?

  2. It is my understanding that any signals going in or coming out of the expansion header must be 1.8 V, otherwise the board will be damaged. Can anyone confirm this? If so, are the I2C signals coming out of the OMAP3450 adequately configured to 1.8 V?

  3. For the input signals going into the GPIO ports, is there a quick and easy way to reduce these signals from 5V to 1.8 V without much hassle? Is it even necessary to do so?

I would appreciate any feedback on any of these questions.

Thank you,

Daniel A. Sosa
University of Texas at El Paso

dasosa@miners.utep.edu wrote:

Hello all,
I am fairly new to the BeagleBoard and I was hoping if someone could answer a couple of questions. I'm trying to connect a couple of devices to the expansion headers. I would appreciate the help.

I can answer one of them, but other people are handling hardware, which I guess doesn't teach me as much ;^)

1. Are the columns in table 17 from the hardware reference manual mutually exclusive? For my project purposes, I need to be able to

Each pin can be independently configured as you like - but remember there are errors in the table (pins 6 & 10, at least). Download sprufa6a (system control module) from TI's omap3530 site.

Refer to the OMAP3530 Technical Reference Manual. http://focus.ti.com/docs/prod/folders/print/omap3530.html

There are registers inside the OMAP3530 that are used to set the functions of each pin on the expansion connector. There is no external HW to the OMAP3530 that controls this. It is all inside the OMAP3530.

Gerald

2. It is my understanding that any signals going in or coming out of the expansion header must be 1.8 V, otherwise the board will be damaged. Can anyone confirm this? If so, are the I2C signals coming out of the OMAP3450 adequately configured to 1.8 V?

If you look at the schematics for the Beagle Board itself, you can see
how they translate between voltages for the I2C bus going to the DVI-D
connector (it's on page 10 of the schematic). You will also need to
add the pull ups for I2C2_[SCL,SDA], which are on page four of the
schematic.

3. For the input signals going into the GPIO ports, is there a quick and easy way to reduce these signals from 5V to 1.8 V without much hassle? Is it even necessary to do so?

Yes, it is necessary.

Quick and easy depends on how each port is used, and your definition
of quick and easy. It should be obvious that you can use something
like the TXS0102 after looking at the schematic, and TI (and many
others) make larger (more bits per part) voltage level translators.

It could also be as simple as using an N-channel FET with the input
pin on the OMAP pulled up (1V8) and connected to the drain on the FET;
connect the source to ground; and connect the gate to the 5V signal
(and you would probably want a weak pull down resistor on the gate
line as well.) This inverts the signal: high on the 5V side is low on
the 1V8 side and low on the 5V side is high on the 1V8 side, which is
usually not be a problem.

-Preston