Indication of 32kHz Clock
There is a bit to indicate whether or not the 32kHz clock input is connected to the LPC47B27x. This bit is located at
bit 0 of the CLOCKI32 register at 0xF0 in Logical Device A. This register is powered by VTR and reset on a VTR
POR.
Bit[0] (CLK32_PRSN) is defined as follows:
0=32kHz clock is connected to the CLKI32 pin (default)
1=32kHz clock is not connected to the CLKI32 pin (pin is grounded).
Bit 0 controls the source of the 32kHz (nominal) clock for the CIR logic, fan tachometer logic, WDT, the LED blink
logic and the “wake on specific key” logic. When the external 32kHz clock is connected, that will be the source for the
CIR logic, fan tachometer, LED and “wake on specific key” logic. When the external 32kHz clock is not connected,
an internal 32kHz clock source will be derived from the 14MHz clock for the CIR logic, fan tachometer, WDT, LED
and “wake on specific key” logic.
The following functions will not work under VTR power (VCC removed) if the external 32kHz clock is not connected.
These functions will work under VCC power even if the external 32kHz clock is not connected.
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CIR wakeup
Wake on specific key
LED blink
Fan tachometer
WDT
Trickle Power Functionality
When the LPC47B27x is running under VTR only (VCC removed), PME wakeup events are active and (if enabled)
able to assert the nIO_PME pin active low. The following lists the wakeup events:
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UART 1 Ring Indicator
UART 2 Ring Indicator
Keyboard data
Mouse data
CIR
Wake on Specific Key Logic
Fan Tachometers (Note)
GPIOs for wakeup. See below.
Note. The Fan Tachometers can generate a PME when VCC=0. Clear the enable bits for the fan tachometers
before removing fan power.
The following requirements apply to all I/O pins that are specified to be 5 volt tolerant.
I/O buffers that are wake-up event compatible are powered by VCC. Under VTR power (VCC=0), these pins may
only be configured as inputs. These pins have input buffers into the wakeup logic that are powered by VTR.
I/O buffers that may be configured as either push-pull or open drain under VTR power (VCC=0), are powered by
VTR. This means, at a minimum, they will source their specified current from VTR even when VCC is present.
The GPIOs that are used for PME wakeup as input are GP10-GP17, GP20-GP22, GP24-GP27, GP30-GP34, GP41,
GP43, GP50-GP57, GP60, GP61. These GPIOs function as follows (with the exception of GP53, GP60 and GP61 -
see below):
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Buffers are powered by VCC, but in the absence of VCC they are backdrive protected (they do not impose a load
on any external VTR powered circuitry). They are wakeup compatible as inputs under VTR power. These pins
have input buffers into the wakeup logic that are powered by VTR.
All GPIOs listed above are for PME wakeup as a GPIO (or alternate function) excluding GP34, which has the IRRX2
function and is used for CIR PME wakeup only. Note that GP32 and GP33 cannot be used for wakeup under VTR
power (VCC=0) since these are the fan control pins which come up as outputs and low following a VCC POR and
Hard Reset. GP53 cannot be used for wakeup under VTR power since this is the TXD2(IRTX) pin which comes up
as output and low following a VTR POR, a VCC POR and Hard Reset. GP43 reverts to the basic GPIO function
when VCC is removed from the part, but its programmed input/output, invert/non-invert and output buffer type is
retained.
SMSC LPC47B27x
- 16 -
Rev. 08-10-04
DATASHEET
SMSC [ SMSC CORPORATION ]
