Hello,
After studying the MSP430FR2422 datasheet and the family datasheet I'm still in doubt how to interpret the RC recommendation for the RST/NMI/SBWTDIO pin. It's mandatory for me to fully understand what( and why) the requirements for this pin are, this to save parts/costs and board space. Even if only to save ONE resistor or ONE capacitor.
Conditions:
- SBW programming interface will be used. This to save I/O pins.
- NMI functionality will not be used.
Datasheet RC recommendation for this pin:
- Pull-up resistance 47k
- Pull-down capacitance 10nF.
When using the SBW programming interface the maximum value for this capacitance is: 1.1nF (otherwise programming tools are not able to drive this 10nF).
1) So why is it allowed to use a smaller capacitance when using SBW programming? contradicts with the 10nF recommendation.
2) Is it important that this pin has a specific Reset timing (minimum RC time)? I was not able to find something about this in the datasheet.
3) Or is this RC combination only used to filter EMI on this pin. Meaning that the RC value's are actually more based on: trace length, nearby switching signals, shielding, ground return path etc.
4) It seems beneficial to me to use the internal RST pull-up resistor (costs). Are there any drawbacks when using this resistor. For sure the tolerance of this internal resistor is big compared to an external pull-up resistor.
Thanks for your help,
Patrick