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A PLC is an industrial microprocessor-based controller with programmable memory used to store program instructions and various functions. [21] It consists of: A processor unit (CPU) which interprets inputs, executes the control program stored in memory and sends output signals, A power supply unit which converts AC voltage to DC,
There is the ability to opt out of APM control on a device-by-device basis, which can be used if a driver wants to communicate directly with a hardware device. Communication occurs both ways; power management events are sent from the BIOS to the APM driver, and the APM driver sends information and requests to the BIOS via function calls.
Some devices may expose such attributes in multiple "pages", as for example one page managing each power supply rail (maybe 3.3V, 5V, 12V, −12V, and a programmable supply supporting 1.0–1.8V). The device may set warning and fault limits, where crossing a limit will alert the host and possibly trigger fault recovery.
The xAPIC was introduced with the Pentium 4, while the x2APIC is the most recent generation of the Intel's programmable interrupt controller, introduced with the Nehalem microarchitecture in November 2008. [17] The major improvements of the x2APIC address the number of supported CPUs and performance of the interface.
Advanced Configuration and Power Interface (ACPI) is an open standard that operating systems can use to discover and configure computer hardware components, to perform power management (e.g. putting unused hardware components to sleep), auto configuration (e.g. Plug and Play and hot swapping), and status monitoring.
The System Management Bus (SMBus or SMB) is a single-ended simple two-wire bus for the purpose of lightweight communication. Most commonly it is found in chipsets of computer motherboards for communication with the power source for ON/OFF instructions.
SCPI commands to an instrument may either perform a set operation (e.g. switching a power supply on) or a query operation (e.g. reading a voltage). Queries are issued to an instrument by appending a question-mark to the end of a command. Some commands can be used for both setting and querying an instrument.
As an example, assume the case of Wake-on-LAN. Traditionally, the OS controls Wake-on-LAN and must call third-party device drivers to enable support on a network card. With the HECI bus, the host is able to assert its request line (REQ#), the ME will assert its grant line (GNT#), and the host can send its message using its serial transmit signal.