Power Management Unit (PMU) is a microcontroller that regulates the power functions of a digital platform. The Microchip has many components similar to the average computer, including firmware and software, memory, CPU, input/output functions, timers to measure time intervals, and analog to digital converters to measure primary battery voltage or computer resources. PMU is one of several items to remain active even when the computer is completely off, supported by a backup battery.
For portable computers, the PMU is responsible for coordinating many functions, including:
- Monitor power connection and battery charging
- Charge the battery if necessary
- Controls power to other integrated circuits
- Shut down unnecessary system components when they are left idle
- Controls sleep and power (on or off)
- Manage interfaces to build on keypads and trackpads on portable computers
- Set real-time clock (RTC)
PMU controls almost every power-consuming function on Apple computers. It constantly runs diagnostics on various power-related operations and checks them against current Energy-Saver settings, enabling PMUs to actively manage power consumption for optimal user performance.
The PMU function can become corrupted over time. If this happens, it may become unresponsive and stop doing the task. Users may not see so many PMU malfunctions as a side effect of corruption, including:
- Failure to enable
- Failure to restore from sleep mode
- Failure to recognize connected devices (FireWire, USB, etc.)
Resetting the PMU in these circumstances can be a relatively quick and easy fix for some of these issues. There is a keyboard shortcut on newer Apple laptops with an internal battery, dubbed "SCOP". This stands for S hift C ontrol O ption P ower. It "reboots" the PMU software to make it work properly. For an Apple laptop with removable battery, resetting the PMU involves unplugging the power adapter, disconnecting the battery, then holding the power button for five seconds. Another improvement related to the PMU is to reset the logic board, where one removes the backup battery on the board for several minutes, then reinstall it, causing the PMU to rearrange itself with clean and fresh parameters (which need to be fixed, if desired, to the state before) during the next Mac OS boot (for ordinary PC users, this is similar to "resetting CMOS").
The PMU is very sensitive and resetting may be required if the backup battery is off. Even plugging the laptop in the wrong order can cause problems (power goes into the outlet first, THEN power to the computer). Do not power off the connected UPS without removing the AC adapter first.
Video Power Management Unit
See also
- Integrated power management circuit (PMIC)
- System Management Unit (SMU)
- System Management Controller (SMC)
Maps Power Management Unit
References
- "Desktop and Portable Systems: Second Edition" Edited by Owen W. Linzmayer ISBNÃ, 0-321-33546-5
External links
- Resetting the PMU on Macbook and MacbookPro computers - contains general information about PMU
Source of the article : Wikipedia
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