RM46L852: Modification of Pull-up or Pull-down resistors during assertion of RESET

TI-CSC

Part Number: RM46L852

Hello E2E Experts,

Good day.

The customer requests confidentiality.

I am writing this case because I need to assign pull-up resistors on the SPI4 pins and pull-down resistors on other pins of the RM46L852 during the RESET process, in other words, when I set the pin nPORRST to value "0".

However, the RM46L852 microcontroller already has got defined default values for each pin as we can see in its datasheet (I attach this feature). Therefore, I would like to know if it is possible to change this default value (I have read in the eFuse Controller section of the User guide that this feature is not possible, but I suppose that it is strange because other microcontrollers implement this feature, so I think that I have misunderstood it).

If this feature is not implemented for the RM46L852 microcontroller, I would like to ask if it is possible to add external pull-up or pull-down resistors. For example, I have added a pull-up resistor of 10 Kohm to SPI4NCS[0 pins and I can see that the signal does not reach exactly the value of 3.3 V, I suppose that this situation is because of the internal pull-up resistor.

On the other hand, I would want to know the value of the internal resistors.

Regards,

CSC

over 2 years ago

0 jagadish gundavarapu over 2 years ago

TI__Guru 70241 points

Hi CSC,

We started working on your issue and will provide an update soon.

Thanks & regards,
Jagadish.

0 jagadish gundavarapu over 2 years ago in reply to jagadish gundavarapu

TI__Guru 70241 points

Hi CSC,

Please refer below thread to understand the PULL state after reset and let me know if you have any further questions.

(+) TMS570LS0332: Build-in PU and PD resistors under and after reset - Arm-based microcontrollers forum - Arm-based microcontrollers - TI E2E support forums

Thanks & regards,
Jagadish.

0 TI-CSC over 2 years ago in reply to jagadish gundavarapu

TI__Genius 12995 points

Hello Jegadish,

Good day.

I just read the post that you sent me. However, I won't program the pull resistor after the reset state instead I would like to know if it is possible to program the pull resistor during the Reset state. Therefore, my questions are the following:

1) Could I change the internal pull-down (default) resistor value for an internal pull-up so that now this internal resistor is a pull-up resistor during the Reset state?

2) Could I use an external resistor if it is not possible changing the default value of the internal resistor? For example, in the picture that attach you, we can see that if I use an external resistor of 10 Kohm, the voltage on the pin will not "0" ( internal pull-down resistor) but will be at 3.2V due to the external pull-up resistor when the microcontroller is in the reset state.

3) Would it be possible to use an external resistor to modify the pull value during Reset state? Or is there a problem with it?

Regards,

CSC

0 jagadish gundavarapu over 2 years ago in reply to TI-CSC

TI__Guru 70241 points

Hello CSC,

Apologies for the delay, as i discussed with internal hardware team so it consumed some time.

TI-CSC said:
1) Could I change the internal pull-down (default) resistor value for an internal pull-up so that now this internal resistor is a pull-up resistor during the Reset state?

Unfortunately, this won't possible.

TI-CSC said:
2) Could I use an external resistor if it is not possible changing the default value of the internal resistor? For example, in the picture that attach you, we can see that if I use an external resistor of 10 Kohm, the voltage on the pin will not "0" ( internal pull-down resistor) but will be at 3.2V due to the external pull-up resistor when the microcontroller is in the reset state.

Yes, you can use external resistor for changing the default internal resistor.

Instead of using type 20uA, use a worst-case scenario (40uA). If this is the case, it causes 0.188 V drop across the 4.7k resistor and results in a Vpin of 3.112. The Vih value for the device is 0.8*Vio = 2.64. This leaves plenty of guardband to ensure proper logical high is registered.

TI-CSC said:
3) Would it be possible to use an external resistor to modify the pull value during Reset state? Or is there a problem with it?

Yes, you can use external pull-up resistor to modify the internal pull value during Reset state. There is no problem, but there can be a unnecessary leakage current between external pull-up and internal pull-down even after the reset state, so we recommend you to disable internal pull-down after reset to eliminate this unnecessary leakage current.

Thanks & regards,
Jagadish.