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‘WAKE ON SPECIFIC KEY’ OPTION
The LPC47B34x has logic to detect a single keyboard scan code for wakeup (PME generation). The
scan code is programmed onto the Keyboard Scan Code Register, a runtime register at offset 0x5F
from the base address located in the primary base I/O address in Logical Device A. This register is
powered by VTR and battery backed up, so it is reset on VBAT POR.
The PME status bit for this event is located in the PME_STS1 register at bit 5 and the PME enable bit
for this event is located in the PME_EN1 register at bit 5. See the Runtime Register section for a
definition of these registers.
Data transmissions from the keyboard consist of an 11-bit serial data stream. A logic 1 is sent at an
active high level. The following table shows the functions of the bits.
BIT
1
2
3
4
5
6
7
8
9
10
11
FUNCTION
Start bit (always 0)
Data bit 0 (least significant bit)
Data bit 1
Data bit 2
Data bit 3
Data bit 4
Data bit 5
Data bit 6
Data bit 7 (most significant bit)
Parity bit (odd parity)
Stop Bit (always 1)
The timing for the keyboard clock and data signals are shown in the “Timing Diagrams” section.
The CLK32_PRSN bit (bit 0 of the CLOCKI32 register at 0xF0 in Logical Device A) will determine the
clock source for this feature when the part is powered by VCC. If the external 32kHz clock is not
connected, the 32kHz internal signal is derived from the 14MHz clock when VCC is active. The 32kHz
clock is used for this feature when the part is under trickle power. This feature will also work when the
part is under trickle power (VCC removed) if the external 32kHz clock is not connected if the ring
oscillator is enabled. See the Intrusion/Oscillator Select register at offset 0x5E in the Runtime
Registers section.
The SPEKEY_EN bit at bit 1 of the CLOCKI32 register at 0xF0 in Logical Device A is used to control
this feature. This bit is used to turn the logic for this feature on and off. It will disable the 32kHz clock
input to the logic. The logic will draw no power when disabled. The bit is defined as follows:
0= “Wake on specific key” logic is on (default)
1= “Wake on specific key” logic is off
Note: The generation of a PME for this event is controlled by the PME enable bit (located in the
PME_EN1 register at bit 5) when the logic for this feature is turned on.