TMP75-Q1: How to send SM_BUS command

Renjith Mohan

Intellectual 520 points

Part Number: TMP75-Q1
Other Parts Discussed in Thread: TMP75

Hello everyone,

I am using TMp75 sensor for real time temperature monitoring, I configured interrupt alert. it works fine.

But i have a doubt how to send the SM_BUS command to the sensor ?

i2c_write(Slave_address,SM_BUS_command) -> is this correct ? if it wrong correct me.

Regards,

Renjith Mohan

over 6 years ago

0 Amit Ashara over 6 years ago

TI__Guru**** 244400 points

Hello Renjith,

I am not sure what "i2c_write(Slave_address,SM_BUS_command)" as this seems to be a very specific MCU question than a sensor question. Please clarify what the "i2c_write(Slave_address,SM_BUS_command)" will do on the bus and what exactly are you trying to do with SMBus command to the sensor.

0 Ren Schackmann over 6 years ago

TI__Mastermind 43815 points

Hi Renjith,

The SMBus commands described in sections 7.3.2.5 and 7.3.2.6 of the TMP75 datasheet must be preceded by the SMBus General Call Address (0.)
i2c_write(0,SM_BUS_command)

Thanks,
Ren

0 Renjith Mohan over 6 years ago in reply to Ren Schackmann

Intellectual 520 points

Hi Ren,

Thank you very much for you reply..!

I tried with writing the device "i2c_write(0x00,0x19)" But i didn't get any response . I am using i2c interrupt for operation.
After write operation is it necessary to perform a read ? How will be the read format for the same? Is there any example code for this ?

Regards,
Renjith

0 Amit Ashara over 6 years ago in reply to Renjith Mohan

TI__Guru**** 244400 points

Hello Renjith,

Can you please connect a scope on the bus to see what transaction is being performed on the bus?

0 Renjith Mohan over 6 years ago in reply to Amit Ashara

Intellectual 520 points

Hi amit,
Currently scope is unavailable,
Kindly relpy
"After write operation is it necessary to perform a read ? How will be the read format for the same? Is there any example code for this ?"

Regards,
Renjith

0 Amit Ashara over 6 years ago in reply to Renjith Mohan

TI__Guru**** 244400 points

Hello Renjith,

Which SMBUS Command are you sending. Is it the General Call or the Alert command?

0 Renjith Mohan over 6 years ago in reply to Amit Ashara

Intellectual 520 points

Hi Amit,

Thank You for your quick response,
I am sending SMBus Alert command (00011001).

Regards,
Renjith

0 Amit Ashara over 6 years ago in reply to Renjith Mohan

TI__Guru**** 244400 points

Hello Renjith,

When the SMBus Alert command is sent, the read has to be done to get the Slave Address of the device which has an Alert asserted. This is given in the timing diagram in Figure-10.

As Ren Schackmann had mentioned earlier in the SMBus General Call command, the slave address in this case would be 0x0C.

0 Renjith Mohan over 6 years ago in reply to Amit Ashara

Intellectual 520 points

Hi Amit,

This is what i understand from your replies,

for sending the command "i2cWrite(0x00,0x0C)",
for reading the response i2cRead(0x0C);

kindly correct me if i am wrong,

Regards,
Renjith

0 Amit Ashara over 6 years ago in reply to Renjith Mohan

TI__Guru**** 244400 points

Hello Renjith,

It should be just " i2cRead(0x0C)"

0 Ren Schackmann over 6 years ago in reply to Amit Ashara

TI__Mastermind 43815 points

SMBus Alert Query is actually another reserved address; it's not used with the General Call Address contrary to my previous response. I apologize for the confusion.

Since ALERT pin from multiple devices can be wire-or into one microcontroller interrupt pin, SMBus provides a method to deduce which device provided the alert. A read transaction sent to the SMBus Alert reserved address (0x0C 7bit, 0x19 8bit, and denoted in Section 7.3.2.5 as 0b00011001) prompts a device asserting ALERT to identify itself so that the I2C Host can service the interrupt. If there is no device asserting ALERT, then there will be no response to this read transaction. The device which does respond should release ALERT upon successfully responding to the SMBus Alert query. See attached image, and note that 0x91 is the 8 bit, read transaction address for the 7 bit 0x48 temperature sensor address.

Thanks,

Ren

0 Renjith Mohan over 6 years ago in reply to Ren Schackmann

Intellectual 520 points

Hi Ren,

Thank You Very much for your Explanation..

Now it worked ..!!

Regards,

Renjith Mohan

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TMP75-Q1: How to send SM_BUS command