# PSoC™ 5, 3 & 1 Forum Discussions

Level 1
Level 1

To whom it may concern,

Would it be possible to provide more details regarding the following excerpt:

- What is the minimum resistor value that can be used as a ‘strong’ pull-up on the MSB?
-> Can it be shorted to either VDD or VSS?
-> Equally what happens if resistor to VDD/VSS is >200k or left open?

- How do the address pins sense the strong pull-up?

- How tolerant is this sense circuitry tolerant to noise?
-> Are decoupling capacitors required?

- What will happen if a resistor value between 330~75KOhms is tied to the address pins?

- Are the 330 Ohms and 75kOhms defined to work over the -40 ~ +85C temperature range?

- Are the Address bits pull up/down resistors only sampled once at power-up?
-> Are there any timings/thresholds for which pull state must comply to?

Look forward to hearing from you.

Many Thanks,
Bhav

1 Solution
Moderator
Moderator

Hello Bhav,

Here are my replies in bold

- What is the minimum resistor value that can be used as a ‘strong’ pull-up on the MSB?

-> Can it be shorted to either VDD or VSS?

-> It can be shorted to either VDD or VSS.

-> Equally what happens if resistor to VDD/VSS is >200k or left open?

-> Since it is open, there is a chance it might be receptive to noise

- How do the address pins sense the strong pull-up?

The pin is driven internally through a resistor, typically 5.6kΩ. If a strong pull up is used, it forces the logic level to which it is connected to. Driving it internally to the opposite logic level will have no effect. In case a weak pull up is used, the logic level follows the internal driver. This way we detect a strong or a weak pull up.

- How tolerant is this sense circuitry tolerant to noise?

-> Are decoupling capacitors required?

Decoupling capacitors are not required, but can be used. Around 100pF should be sufficient.

- What will happen if a resistor value between 330~75KOhms is tied to the address pins?

We cannot be sure if it will be detected as strong or a weak pull-up. Hence, it is not recommended.

- Are the 330 Ohms and 75kOhms defined to work over the -40 ~ +85C temperature range?

Yes. Kindly note that the resistors value must meet the specifications across -40°C ~ +85°C. Hence, ensure the Tempco of the resistors is appropriate.

- Are the Address bits pull up/down resistors only sampled once at power-up?

-> Are there any timings/thresholds for which pull state must comply to?

Yes, the I2C Address setting pull-up / pull-down resistors are sampled once at power-up. There are no other timings / thresholds to consider. Kindly do not use capacitors of more than 100pF on these lines. They may not reach final value when the device senses them, which is roughly around 200ms from power-up.

Thanks, and best regards,

Sampath Selvaraj

Moderator
Moderator

Hello Bhav,

Here are my replies in bold

- What is the minimum resistor value that can be used as a ‘strong’ pull-up on the MSB?

-> Can it be shorted to either VDD or VSS?

-> It can be shorted to either VDD or VSS.

-> Equally what happens if resistor to VDD/VSS is >200k or left open?

-> Since it is open, there is a chance it might be receptive to noise

- How do the address pins sense the strong pull-up?

The pin is driven internally through a resistor, typically 5.6kΩ. If a strong pull up is used, it forces the logic level to which it is connected to. Driving it internally to the opposite logic level will have no effect. In case a weak pull up is used, the logic level follows the internal driver. This way we detect a strong or a weak pull up.

- How tolerant is this sense circuitry tolerant to noise?

-> Are decoupling capacitors required?

Decoupling capacitors are not required, but can be used. Around 100pF should be sufficient.

- What will happen if a resistor value between 330~75KOhms is tied to the address pins?

We cannot be sure if it will be detected as strong or a weak pull-up. Hence, it is not recommended.

- Are the 330 Ohms and 75kOhms defined to work over the -40 ~ +85C temperature range?

Yes. Kindly note that the resistors value must meet the specifications across -40°C ~ +85°C. Hence, ensure the Tempco of the resistors is appropriate.

- Are the Address bits pull up/down resistors only sampled once at power-up?

-> Are there any timings/thresholds for which pull state must comply to?

Yes, the I2C Address setting pull-up / pull-down resistors are sampled once at power-up. There are no other timings / thresholds to consider. Kindly do not use capacitors of more than 100pF on these lines. They may not reach final value when the device senses them, which is roughly around 200ms from power-up.

Thanks, and best regards,

Sampath Selvaraj