IBF
(Input Buffer Full)- This flag is set to 1 whenever the host system writes data into the input data
register. Setting this flag activates the LPC47B27x CPU's nIBF (MIRQ) interrupt if enabled.
When the LPC47B27x CPU reads the input data register (DBB), this bit is automatically reset and
the interrupt is cleared. There is no output pin associated with this internal signal.
OBF
(Output Buffer Full) - This flag is set to whenever the LPC47B27x CPU write to the output data
register (DBB). When the host system reads the output data register, this bit is automatically
reset.
EXTERNAL CLOCK SIGNAL
The LPC47B27x Keyboard Controller clock source is a 12 MHz clock generated from a 14.318 MHz clock.
The reset pulse must last for at least 24 16 MHz clock periods. The pulse-width requirement applies to
both internally (Vcc POR) and externally generated reset signals. In powerdown mode, the external clock
signal is not loaded by the chip.
DEFAULT RESET CONDITIONS
The LPC47B27x has one source of hardware reset: an external reset via the nPCI_RESET pin. Refer to
Table 46 for the effect of each type of reset on the internal registers.
Table 54 - Resets
HARDWARE RESET
DESCRIPTION
(nPCI_RESET)
KCLK
KDAT
MCLK
MDAT
Host I/F Data Reg
Host I/F Status Reg
Low
Low
Low
Low
N/A
00H
N/A: Not Applicable
GATEA20 AND KEYBOARD RESET
The LPC47B27x provides two options for GateA20 and Keyboard Reset: 8042 Software Generated
GateA20 and KRESET and Port 92 Fast GateA20 and KRESET.
PORT 92 FAST GATEA20 AND KEYBOARD RESET
Port 92 Register
This port can only be read or written if Port 92 has been enabled via bit 2 of the KRST_GA20
Register (Logical Device 7, 0xF0) set to 1.
This register is used to support the alternate reset (nALT_RST) and alternate A20 (ALT_A20) functions.
Name
Port 92
92h
Location
Default Value
Attribute
Size
24h
Read/Write
8 bits
Port 92 Register
Bit
7:6
5
Function
Reserved. Returns 00 when read
Reserved. Returns a 1 when read
Reserved. Returns a 0 when read
Reserved. Returns a 0 when read
Reserved. Returns a 1 when read
4
3
2
1
ALT_A20 Signal control. Writing a 0 to this bit causes the ALT_A20 signal to be
SMSC LPC47B27x
- 103 -
Rev. 08-10-04
DATASHEET
SMSC [ SMSC CORPORATION ]
