Mico Reset

[gogoman]

hi most micro have internal power on reset and VCC monitoring, what advantage would there be to use an external reset IC?


thanks

[ogden]

Usually you are fine with built-in monitor, yet there are some cases you may need external monitor: 1) voltage ramp-up speed is too slow for MCU brownout circuit 2) MCU brownout voltage treshold shall be changed but MCU do not have means for that, like MSP430 F1/F2 series. Fun fact that AVR users rarely ask this question - because even AtTiny have programmable BOR treshold fuses.

Search internet for "msp430 flash corruption" - you will see people suggesting external monitor as solution Here's story: Msp430 n00bs sometimes immediately at the startup set internal clock from default ~1 MHz to 16MHz maximum. Thing is that BOR treshold is 0.8V and max allowed frequency at this voltage is 1MHz, for 16MHz at least 3V needed Obviously "overclocked" msp430 (F1/F2 maybe other as well) may intermittently crash on power-on or even erase some code flash segment. So, if you have facepalm moment and there's no time or MCU resources to fix power-on problem in firmware by simply adding delay or coding "software BOR treshold" using ADC, you can quickly slap-in external 3.0V supervisor.

[Dabbot]

The use of an external IC allows you to select a particular POR / BOR voltage which may not be supported by the microcontroller. You might also have other devices which need to be held in reset so your circuit can operate reliably after POR / BOR conditions.

[David Hess]

An external reset IC can also monitor for conditions which are determined to require reset like loss of AC power or a drop at the input to the regulator which the processor POR/BOR cannot see directly in real time.

[ogden]

An external reset IC can also monitor for conditions which are determined to require reset like loss of AC power or a drop at the input to the regulator which the processor POR/BOR cannot see directly in real time.

Well, yes. Some (dumbed down) devices may need such reset terror Usually you would want to know source of failure. Power loss detection, logging and graceful shutdown can be implemented quite easily. All you need - properly sized bulk capacitors for MCU power supply so there is time to detect power fail (using IRQ), execute housekeeping, log/register type of failure and go into powerfail mode - wait for power restore to resume operations or POR/BOR reset to kick in.

[David Hess]

An external reset IC can also monitor for conditions which are determined to require reset like loss of AC power or a drop at the input to the regulator which the processor POR/BOR cannot see directly in real time.

Well, yes. Some (dumbed down) devices may need such reset terror Usually you would want to know source of failure. Power loss detection, logging and graceful shutdown can be implemented quite easily. All you need - properly sized bulk capacitors for MCU power supply so there is time to detect power fail (using IRQ), execute housekeeping, log/register type of failure and go into powerfail mode - wait for power restore to resume operations or POR/BOR reset to kick in.

An IRQ is a much better way but not all microcontrollers and environments will support it.