LPC47N227TQFP Standard Microsystems (SMSC), LPC47N227TQFP Datasheet - Page 118

• Manufacturer Part Number: LPC47N227TQFP
• Manufacturer: Standard Microsystems (SMSC)

Specifications of LPC47N227TQFP

• Lead Free Status / RoHS Status: Not Compliant

PCI CLKRUN SUPPORT
Overview
The LPC47N227 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. The LPC47N227 nCLKRUN signal is on
TQFP/STQFP pin number 28. See FIGURE 3 for an example of a typical system implementation using
nCLKRUN.
If the LPC47N227 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.
nCLKRUN for Serial IRQ
The LPC47N227 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.
nCLKRUN for nLDRQ
nCLKRUN support is also provided in the LPC47N227 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.
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 LPC47N227 asserts or de-asserts an
interrupt or asserts a DMA request, and nCLKRUN is sampled “high”, the LPC47N227 requests the
restoration of the clock by asserting the nCLKRUN signal asynchronously (Table 47). The LPC47N227
holds nCLKRUN low until it detects two rising edges of the clock. After the second clock edge, the
LPC47N227 disables the open drain driver (FIGURE 4).
The LPC47N227 will not assert nCLKRUN under any conditions if SIRQ_CLKRUN_EN is inactive (“0”).
The SIRQ_CLKRUN_EN bit is D7 in CR29.
The LPC47N227 will not assert nCLKRUN if it is already driven low by the central resource; i.e., the
PCI CLOCK GENERATOR in FIGURE 3. The LPC47N227 will not assert nCLKRUN unless the line
has been deasserted for two successive clocks; i.e., before the clock was stopped (FIGURE 4).
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