i2c not working

David Sabol

Other Parts Discussed in Thread: HALCOGEN, TMS570LS1227

Hi,

I'm trying to get i2c set up, but it is not working (I don't get any data over the SDA or SCL lines).

I am using CCS6, halcogen 4.1, tms570LS1227 and interfacing with a microchip MCP23008 I/o expander.

In Halcogen I have enabled the i2c driver and selected i2c on the pinmux tab. On the i2c global tab I have it set for 7 bit addr mode, enable master mode, transmitter, 8 bit count, 8 data count, and enable free data format (I have tried without free data format as well).

To read from a register on the slave device, I need to send 8 bits of the device opcode (0x4D) followed by the register address (0x00).

I'm sure I'm just missing something stupid, but I can't see it. Any help is appreciated.

	i2cInit();
	i2cSetStart(i2cREG1);
	i2cSendByte(i2cREG1, 0x4D);
    i2cSendByte(i2cREG1, 0x00);

    while(i2cIsRxReady(i2cREG1)){};

    data = i2cReceiveByte(i2cREG1);
    i2cSetStop(i2cREG1);

over 10 years ago

0 Charles Tsai over 10 years ago

TI__Guru**** 191886 points

Hello David,

If you have not seen anything on SCL and SDA then please check if you configure IOMM module to bring out the I2C. I2C is multiplexed with MibSPI3nCS. By default, MiSPI2nCS are the primary pins. Also check on the scope if the slave is returning the ACK. I also assume you have proper pullup on both SCL and SDA.

0 Charles Tsai over 10 years ago in reply to Charles Tsai

TI__Guru**** 191886 points

Typo in my reply. I meant MibSPI3nCS are the primary pins.

0 David Sabol over 10 years ago in reply to Charles Tsai

Genius 4850 points

Thanks for your reply.

I have i2c enabled on the pin mux tab in halcogen, so I2C_SCL and I2C_CDA are selected and not the Mibspo3 CS.

In Halcogen pull up is selected for the SDA and SCL pins, but it does not look like there are actual pull ups in the schematic.

I don't see anything coming out from either line.

0 Charles Tsai over 10 years ago in reply to David Sabol

TI__Guru**** 191886 points

Hello David,

What I meant by pullup is the external pull resistor on the bus. Do you have this pullup on both the SCL and SDA bus?

0 David Sabol over 10 years ago in reply to Charles Tsai

Genius 4850 points

I don't see any pull ups on the schematic, but I'll have to check with the ee who designed it. I think he is on vacation until tomorrow. I'll post again when I know for sure.

Thanks for your help

0 Charles Tsai over 10 years ago in reply to David Sabol

TI__Guru**** 191886 points

Hello David,

At the physical layer, both SCL and SDA lines are of open-drained design, thus pullup resistors are needed. The I2C module will drive dominant logic 0 (pulling to the ground) on these two lines only. Logic 1 is by letting the line float with the pullup resistor.

0 David Sabol over 10 years ago in reply to Charles Tsai

Genius 4850 points

The SCL and SDA lines each have 2.2K pull ups to 3.3V

0 Charles Tsai over 10 years ago in reply to David Sabol

TI__Guru**** 191886 points

Hello,

I created a small example with only the master transmitter. The example's only intention is to illustrate that SCL and SDA are being driven by the I2C module. Since I don't have a slave, I set the EMDR register to 0x2 which is to ignore NACK.

I can see both the SCL and SDA on the bus. I use a 2k pullup. Can you try the example and see if you can see any activity on the SCL and SDA?

8475.LS31x_I2C_No_ACK.zip

0 David Sabol over 10 years ago in reply to Charles Tsai

Genius 4850 points

Thanks for the example. It looks like it was a halcogen setup issue. I can see activity on both lines now.

Thanks for your help!

0 Charles Tsai over 10 years ago in reply to David Sabol

TI__Guru**** 191886 points

Glad that see that it is working on your side now.

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i2c not working