Other Parts Discussed in Thread: MSP-EXP430G2ET
Hi Sirs
With PCA9548A, MCU would like to control 4 sensors with same I2C ID.
=> How to evaluate the I2C time tolerance are enough?
PS. Attached are the MCU, Sensors time index.
Sincerely
Jax
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Hi Sirs
With PCA9548A, MCU would like to control 4 sensors with same I2C ID.
=> How to evaluate the I2C time tolerance are enough?
PS. Attached are the MCU, Sensors time index.
Sincerely
Jax
The values of the MCU do not conform to the I²C specifications. Which MCU is this?
We change MCU to MSP-EXP430G2ET demo kit
Sensor(Standard mode)
=> Data hold time_max = 3450ns
=> Data setup time_min = 250ns
=> tfall_Max = 300ns
=> trise_Max = 1000ns
These values are compatible with the limits specified in the I²C specification (for standard mode, i.e., up to 100 kHz). So all I²C-compatible devices will work. The MSP430 is I²C compatible.
The PCA9548A does not change the timing. (It slightly increases the bus capacitance, but this is just the same effect as slightly longer traces.)
Hi Jax,
I agree with Clemens on what he has responded thus far.
I have included the I2C specs from the standard. Please let me know if you have further questions.
Are your Trise/Tfall times flipped?
Regards,
Tyler
Hi Clemens
1. Goal: Check MCU, I2C switcher, Sensor could follow I2C SPEC(provided by Tyler)
2. According to SPEC,
a. Where to describe MSP430G2x53 to follow I2C compatible?
=> I only could find the I2C time index in USCI (I2C Mode) (above figure 20).
b. Where to describe PCA9548A does not change the timing?
=> I only could find the I2C time index like chp6.6
=> Does it have switch delay?
c. Sensor trise & tfall is recheck to following index
Sensor(Standard mode)
=> Data hold time_max = 3450ns
=> Data setup time_min = 250ns
=> trise_Max = 1000ns
=> tfall_Max = 300ns
Hi Jax,
a. Where to describe MSP430G2x53 to follow I2C compatible?
=> I only could find the I2C time index in USCI (I2C Mode) (above figure 20).
These timing specs from the datasheet look to be I2C compatible up to 400kHz. This looks good to me. Rise time is determined by external pull-up resistance and the strength of the open drain driver.
b. Where to describe PCA9548A does not change the timing?
=> I only could find the I2C time index like chp6.6
=> Does it have switch delay?
page 7 of the datasheet shows the I2C standards that this device abides by to be I2C compliant.
When you are talking about switch delay, are you talking about the time it takes after a successful ACK for the switches to change state? I don't believe we spec this in the datasheet.
If you are talking about prop delay from switch input to switch output, this is defined in the datasheet.
c. Sensor trise & tfall is recheck to following index
Sensor(Standard mode)
=> Data hold time_max = 3450ns
=> Data setup time_min = 250ns
=> trise_Max = 1000ns
=> tfall_Max = 300ns
The sensor looks to be I2C compliant with the timing specs provided here. I compared these values to the standard mode of I2C, and the max and min timings are within the spec.
Regards,
Tyler