MM9Z1638D1 cranking mode

[mihir_rajput]

Hello,

I am thinking about using "cranking mode" for preserving contents of RAM in case of under voltage on MM9Z1638D1. Per the reference manual, I can enter cranking mode by writing 0x0303 to PCR_CTL. The flow chart attached here mentions entering cranking mode on UVI or undervoltage interrupt. But I couldn't find vector address for UVI in the reference manual. My initial thought was to write an UVI service routine. Can you help me with this?

Secondly, how to get out of cranking mode?

Finally, once the power on reset threshold is reached the contents of RAM become invalid?

[Q_man]

Hi,

I strongly recommend to NOT use the cranking mode feature. It would be better to analyze which issue you are trying to solve and to find an alternative approach!

I'm not aware of any customer using this feature and I have not used it myself. I expect to have many corner cases of external conditions (e.g. dV/dt of VSUP) and SW handling the process of entering low power mode and exiting it again. So I will not be of much help here.

The UVI is related to the analog die VSUP monitoring. It will typically occur at 5.2V (see Datasheet Table 12. Static electrical characteristics - power supply) and will issue an D2D interrupt if enabled see 6.7.2.4.1Undervoltage Interrupt (UVI)).

The RAM is initialize during the uC Reset to all zeros. This is required to avoid any unintentional ECC errors (see  6.8.3.4 Memory initialization)

Rgds

W.

[Q_man]

Leaving "cranking mode" will be through wakeup from STOP condition! E.g. after predefined time.

W.