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INA740B: Condition of ending of HS mode other than STOP condition.

Hideki Hayashi1
Expert 8220 points
Part Number: INA740B
Other Parts Discussed in Thread: INA740

Hi team,

From 7.5.1.2, HS I2C require MCU to send 00001XXX by host controller in less than fast (400kHz) mode. After that, how long does HS mode last? It will not end by STOP condition, there are no other event triggering to end HS mode, correct?

Also, do you have a waveform which describe the code 00001XXX? Visible image is easier to understand.

Best regards,

Hayashi

  • 0
    TI__Mastermind 32395 points

    Hey Hayashi,

    Once the High speed (HS) mode is enabled within the device, it will remain enabled indefinitely as long as the host uses repeated start conditions and device remains powered on. Only once the host sends a STOP condition, then the device will switch back to fast or standard (F/S) mode.

    Once device is in high-speed mode, it must adhere to the protocol rules.

    Putting the device into HS mode should look like this below. The red section is host sending the HS code in standard or fast speed mode. After the 8th bit the device does not acknowledge and SDA is pulled up. The SCL also is pulled back up. A STOP condition needs to be avoided here an for as long as HS mode is needed. After this, host initiates a repeated start condition and begins normal read/write communication without stop conditions.

    Sincerely,

    Peter

  • 0 in reply to Peter Iliya
    TI__Expert 8220 points

    Hi Peter,

    Thank you! I think I can understand. If customer wants to read 4 INA740 (I2C address: 0x40, 0x41, 0x44, 0x45) repeatedly and read "measured current" (0x07), is below I2C message is correct?

    Writing the appropriate value to the register pointer for 0x40, then writing for 0x41, writing for 0x44, writing for 0x45, and then entering HS mode, and then repeating READ respectively. See the attachment for easier understanding.

    INA740_I2C Timing Chart.xlsx

    Best regards,

    Hayashi

  • 0 in reply to Hideki Hayashi1
    TI__Mastermind 32395 points

    Hellp,

    This is acceptable method. Although you may need enable HS mode for each individual INA740 by writing the HS code right after the INA740 address byte.

    Sincerely,

    Peter

  • 0 in reply to Peter Iliya
    TI__Expert 8220 points

    Hi Peter,

    If so, I think customer sequence doesn't work. Customer should send as below when they wants to enter HS mode respectively, correct?

    0x40 -> 0001XXX -> 0x41 -> 0001XXX -> 0x44 -> 0001XXX -> 0x45 -> 0001XXX

    Best regards,

    Hayashi

  • 0 in reply to Hideki Hayashi1
    TI__Mastermind 32395 points

    Hey Hideki,

    You do not need to specify an address when sending out the HS code. Sending out the HS code will set all INA740's on the bus into HS mode. Here is a link to another post for reference.

    https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/983578/ina231evm-i2c-high-speed-mode

    Sincerely,

    Peter