LPC47S45X datasheet(21/259 Pages) SMSC

21 / 259 page

SMSC DS – LPC47S45x

Page 21 of 259

Rev. 07/09/2001

DATASHEET

Bit[0] controls the source of the 32kHz (nominal) clock for the RTC, 40 MHz clock output, fan tachometer logic, the

LED blink logic, the WDT, and the “wake on specific key” logic. When an external 32kHz clock source is connected,

that will be the source for the RTC, 40 MHz clock output, fan tachometer, LED, WDT and “wake on specific key” logic.

When an external 32kHz clock source is not connected, an internal 32kHz clock source will be derived from the

14MHz clock for the RTC, 40MHz clock output, fan tachometer, LED, WDT and “wake on specific key” logic.

The following functions will not work under VTR power (VCC removed) if an external 32kHz clock source is not

connected. These functions will work under VCC power even if an external 32kHz clock source is not connected.

Fan Tachometer

Wake on specific key

LED blink

WDT

40MHz clock output

RTC

5.6

XOSEL

The XOSEL signal is used to differentiate between a single-input 32kHz signal driven on the CLKI32 pin or an

oscillator connected between XTAL1 and XTAL2. If a single-input 32kHz signal is connected to the CLKI32 pin, the

XOSEL pin should be pulled up to VTR. (A 10k

Ω pull-up resistor is suggested.) If a crystal oscillator is connected

across XTAL1 and XTAL2 then the XOSEL pin should be left unconnected. There is an internal pulldown on this pin

that will keep this pin low when not in use. If no external clock source is supplied, then Bit[0] of the Clock Select

determines if the 32kHz clock source is supplied externally or if it is derived from the 14MHz clock input. The

following table summarizes the state of the 32 kHz clock inputs and the XOSEL pin.

32KHZ CLOCK INPUT

XOSEL

BIT[0] (See Note)

(CLK32_PRSN)

No external 32kHz clock input or XTAL

The 32kHz clock source derived internally

from 14MHz input.

No Connect

(see Note1)

32kHz oscillator connected between

XTAL1 and XTAL2 (default) (see Note1)

No Connect

(see Note1)

Single-input, external 32kHz clock input

driven on the CLKI32 pin

Pull-up to VTR

No external 32kHz clock input or XTAL

The 32kHz clock source derived internally

from 14MHz input.

Pull-up to VTR

Note:

Bit[0] is located in the Clock Select register found in Logical Device A at offset 0xF0.

Note 1:

When the XOSEL pin is left unconnected (i.e., No Connect), the XTAL2/CLKI32 pin is an output and must

not

be grounded.

5.7

Trickle Power Functionality

When the LPC47S45x is running under VTR only, the PME wakeup events are active and (if enabled) able to assert

the IO_PME# pin active low. The following lists the wakeup events:

UART 1 Ring Indicator

UART 2 Ring Indicator

Keyboard data

Mouse data

Wake on Specific Key Logic

Fan Tachometer (Note)

nPB_IN

RTC Alarm

LPC47S45X Datasheet(PDF) 21 Page - SMSC Corporation

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