LPC47N237-MD datasheet(72/138 Pages) SMSC

72 / 138 page

3.3v I/O Controller for Port Replicators and Docking Stations

Revision 0.3 (10-26-04)

Page 72

SMSC DS – LPC47N237

DATASHEET

Chapter 12 PCI CLKRUN Support

12.1

Overview

The LPC47N237 supports the PCI nCLKRUN signal. nCLKRUN is used to indicate the PCI clock status as

well as to request that a stopped clock be started. Figure 12.1 for an example of a typical system

implementation using nCLKRUN.

If the LPC47N237 SIRQ_CLKRUN_EN signal is disabled, it will disable the nCLKRUN support related to

nLDRQ in addition to disabling the SER_IRQ and the nCLKRUN associated with SER_IRQ.

nCLKRUN is an open drain output and an input. Refer to the PCI Mobile Design Guide Rev 1.0 for a

description of the nCLKRUN function.

12.2

nCLKRUN for Serial IRQ

The LPC47N237 supports the PCI nCLKRUN signal for the Serial IRQs. If an SIO interrupt occurs while

the PCI clock is stopped, nCLKRUN is asserted before the serial interrupt signal is driven active.

See “Using nCLKRUN” section below for more details.

12.3

nCLKRUN for nLDRQ

nCLKRUN support is also provided in the LPC47N237 for the nLDRQ signal. If a device requests DMA

service while the PCI clock is stopped, nCLKRUN is asserted to restart the PCI clock. This is required to

drive the nLDRQ signal active.

See “Using nCLKRUN” section for more details.

12.4

Using nCLKRUN

If nCLKRUN is sampled “high”, the PCI clock is stopped or stopping. If nCLKRUN is sampled “low”, the

PCI clock is starting or started (running). If a device in the LPC47N237 asserts or de-asserts an interrupt

or asserts a DMA request, and nCLKRUN is sampled “high”, the LPC47N237 requests the restoration of

the clock by asserting the nCLKRUN signal asynchronously (Figure 12.2).

The LPC47N237 holds

nCLKRUN low until it detects two rising edges of the clock. After the second clock edge, the LPC47N237

disables the open drain driver (Figure 12.2).

The LPC47N237 will not assert nCLKRUN under any conditions if SIRQ_CLKRUN_EN is inactive (“0”).

The SIRQ_CLKRUN_EN bit is D7 in CR29.

The LPC47N237 will not assert nCLKRUN if it is already driven low by the central resource; i.e., the PCI

CLOCK GENERATOR in Figure 12.1. The LPC47N237 will not assert nCLKRUN unless the line has been

deasserted for two successive clocks; i.e., before the clock was stopped (Figure 12.2).

LPC47N237-MD Datasheet(PDF) 72 Page - SMSC Corporation