LPC defines the protocol for an electrical interface between motherboard components.
No connector or mechanical interface is defined by the LPC interface.
The LPC interface was meant to be an interim solution as the ISA bus was being phased out.
Providing a software compatible ISA bus, which really used a minimum hardware [low pin count] interface.
LPC was meant to facilitate the industry's transition toward legacy free systems [legacy free means no ISA bus].
The Low Pin Count [LPC] Bus, may also be called PPC [undefined acronym].
This may be a legacy interface as the ISA and PCI buses are replaced by the PCIe interface.
The document is Low Pin Count (LPC) Interface Specification, Revision 1.1, Aug 2002 [initial release in 1998]
The SST 49LF040B, 4 Mbit Flash is an example of an IC using the Low Pin Count [LPC] interface.
A 32-pin PLCC SST49LF040B 4Meg [512k x 8] Flash IC, attached to a Printed Wiring Board [PWB] is shown left.
Low Pin Count Pinout
In LPC mode, communication between the Host and the
49LF040B occurs via the 4-bit I/O communication signals,
LAD[3:0] and LFRAME#.
The 49LF040B detects the start of an LPC cycle by reading the START field contents; a 0000b indicates the beginning of an LPC memory cycle.
There are several other optional signals [not used with the 49LF040] which include;
LDRQ#. Encoded DMA/Bus Master Request; indicating a peripheral needs a DMA.
SERIRQ. Providing interrupt support to peripherals.
CLKRUN#. Same as PCI CLKRUN#, used to stop the PCI bus.
LPME#. LPC Power Management Event, similar to PCI PME# to wake up from a low-power state.
It does appear that the last revision of the Low Pin Count interface specification was released by Intel in 2002.
So the interface would be considered a legacy interface standard, out-dated, if not obsolete.
No longer required as the ISA buses are long gone, and the PCI interfaces are also disappearing.
The LPC specification makes reference to an X-bus which seems to be an undefined reference to a ISA-to-PCI bridge.
Although, because the document does not define what the X-bus is, it's a bit hard to tell what the X-bus relates to.
In any even the ISA interface is obsolete and has been out-dated fro more than 10 years.
The PCI bus is also out-dated, having been replaced by the PCIe bus more than half a dozen years ago.
In other words if the ISA bus is obsolete and no longer used, there is no need to bridge the interface between ISA and PCI.
However a number of other interfaces call out the Low Pin Count signals.
Their attempt to produce a legacy free standard which would not support legacy [ISA] functionality.
COM Express is an example of a standard using the LPC interface, instead of defining PS/2 keyboard/mouse, serial ports, and parallel ports.
COM Express is an embedded computer board standard, released around 2004.
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