initialization time, either RESET must be held active for sufficient time to allow the oscillator to stabilize.
Program execution will resume as above.
Interrupts
The LPC47S42x provides the two 8042 interrupts: IBF and the Timer/Counter Overflow.
Memory Configurations
The LPC47S42x provides 2K of on-chip ROM and 256 bytes of on-chip RAM.
Register Definitions
Host I/F Data Register
The Input Data register and Output Data register are each 8 bits wide. A write to this 8 bit register will
load the Keyboard Data Read Buffer, set the OBF flag and set the KIRQ output if enabled. A read of
this register will read the data from the Keyboard Data or Command Write Buffer and clear the IBF flag.
Refer to the KIRQ and Status register descriptions for more information.
Host I/F Status Register
The Status register is 8 bits wide. Table 47 shows the contents of the Status register.
Table 47 - Status Register
D7
D6
D5
D4
UD
UD
UD
UD
Status Register
This register is cleared on a reset. This register is read-only for the Host and read/write by the LPC47S42x
CPU.
UD
Writable by LPC47S42x CPU. These bits are user-definable.
C/D
(Command Data)-This bit specifies whether the input data register contains data or a command
(0 = data, 1 = command). During a host data/command write operation, this bit is set to "1" if
SA2 = 1 or reset to "0" if SA2 = 0.
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 LPC47S42x CPU's nIBF (MIRQ) interrupt if enabled.
When the LPC47S42x 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 LPC47S42x 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 LPC47S42x 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.
125
D3
C/D
D2
UD
D1
IBF
D0
OBF