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Low Pin Count
The Low Pin Count bus, or LPC bus, is used on IBM-compatible personal computers to connect low-bandwidth devices to the CPU, such as the boot ROM, "legacy" I/O devices (integrated into a super I/O chip), and Trusted Platform Module (TPM). "Legacy" I/O devices usually include serial and parallel ports, PS/2 keyboard, PS/2 mouse, and floppy disk controller.
Most PC motherboards with a LPC bus have either a Platform Controller Hub (PCH) or a southbridge chip, which acts as the host and controls the LPC bus. All other devices connected to the physical wires of the LPC bus are peripherals.
== Overview ==
The LPC bus was introduced by Intel in 1998 as a software-compatible substitute for the Industry Standard Architecture (ISA) bus. It resembles ISA to software, although physically it is quite different. The ISA bus has a 16-bit wide data bus and a 24-bit address bus that can be used for both 16-bit I/O port addresses and 24-bit memory addresses; both run at speeds up to 8.33 MHz. The LPC bus uses a heavily multiplexed four-bit-wide bus operating at four times the clock speed (33.3 MHz) to transfer addresses and data with similar performance.
LPC's main advantage is that the basic bus requires only seven signals, greatly reducing the number of pins required on peripheral chips. An integrated circuit using LPC will need 30 to 72 fewer pins than its ISA equivalent. It is also easier to route on modern motherboards, which are often quite crowded. The clock rate was chosen to match that of PCI in order to further ease integration. Also, LPC is intended to be a motherboard-only bus. No connector is defined, and no LPC peripheral daughterboards are available, except motherboard-specific Trusted Platform Modules (TPMs).〔 Device discovery is not supported; since only motherboard devices or specific models of TPM are connected, the host firmware (BIOS, UEFI) image will include a static description of any devices and their I/O addresses expected to be present on a particular motherboard.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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