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LPC47B272QFP

100 Pin Enhanced Super I/O Controller with LPC Interface

SMSC -> Microchip 

LPC Cycles

The following cycle types are supported by the LPC protocol.

Cycle Type

I/O Write

I/O Read

DMA Write

DMA Read

Transfer Size

1 Byte

1 Byte

1 Byte

1 Byte

LPC47B27x ignores cycles that it does not support.

Field Definitions

The data transfers are based on specific fields that are used in various combinations, depending on the cycle type.

These fields are driven onto the LAD[3:0] signal lines to communicate address, control and data information over the

LPC bus between the host and the LPC47B27x. See the Low Pin Count (LPC) Interface Specification Revision 1.0

from Intel, Section 4.2 for definition of these fields.

nLFRAME Usage

nLFRAME is used by the host to indicate the start of cycles and the termination of cycles due to an abort or time-out

condition. This signal is to be used by the LPC47B27x to know when to monitor the bus for a cycle.

This signal is used as a general notification that the LAD[3:0] lines contain information relative to the start or stop of a

cycle, and that the LPC47B27x monitors the bus to determine whether the cycle is intended for it. The use of

nLFRAME allows the LPC47B27x to enter a lower power state internally. There is no need for the LPC47B27x to

monitor the bus when it is inactive, so it can decouple its state machines from the bus, and internally gate its clocks.

When the LPC47B27x samples nLFRAME active, it immediately stops driving the LAD[3:0] signal lines on the next

clock and monitor the bus for new cycle information.

The nLFRAME signal functions as described in the Low Pin Count (LPC) Interface Specification Revision 1.0.

I/O Read and Write Cycles

The LPC47B27x is the target for I/O cycles. I/O cycles are initiated by the host for register or FIFO accesses, and will

generally have minimal Sync times. The minimum number of wait-states between bytes is 1. EPP cycles will depend

on the speed of the external device, and may have much longer Sync times.

Data transfers are assumed to be exactly 1-byte. If the CPU requested a 16 or 32-bit transfer, the host will break it

up into 8-bit transfers.

See the Low Pin Count (LPC) Interface Specification Reference, Section 5.2, for the sequence of cycles for the I/O

Read and Write cycles.

DMA Read and Write Cycles

DMA read cycles involve the transfer of data from the host (main memory) to the LPC47B27x. DMA write cycles

involve the transfer of data from the LPC47B27x to the host (main memory). Data will be coming from or going to a

FIFO and will have minimal Sync times. Data transfers to/from the LPC47B27x are 1, 2 or 4 bytes.

See the Low Pin Count (LPC) Interface Specification Reference, Section 6.4, for the field definitions and the

sequence of the DMA Read and Write cycles.

DMA Protocol

DMA on the LPC bus is handled through the use of the nLDRQ lines from the LPC47B27x and special encodings on

LAD[3:0] from the host.

The DMA mechanism for the LPC bus is described in the Low Pin Count (LPC) Interface Specification Revision 1.0.

SMSC LPC47B27x

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DATASHEET

Rev. 04-17-07

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