6.13.1 Keyboard Interface
The LPC47M14x LPC interface is functionally compatible with the 8042 style host interface. It consists of the D0-7 data
signals; the read and write signals and the Status register, Input Data register, and Output Data register. Table 50
shows how the interface decodes the control signals. In addition to the above signals, the host interface includes
keyboard and mouse IRQs.
Table 50 – I/O Address Map
ADDRESS
COMMAND
Write
BLOCK
KDATA
KDATA
KDCTL
KDCTL
FUNCTION (NOTE 1)
Keyboard Data Write (C/D=0)
Keyboard Data Read
Keyboard Command Write (C/D=1)
Keyboard Status Read
0x60
Read
Write
Read
0x64
Note 1: These registers consist of three separate 8 bit registers. Status, Data/Command Write and Data Read.
Keyboard Data Write
This is an 8 bit write only register. When written, the C/D status bit of the status register is cleared to zero and the IBF
bit is set.
Keyboard Data Read
This is an 8 bit read only register. If enabled by "ENABLE FLAGS", when read, the KIRQ output is cleared and the OBF
flag in the status register is cleared. If not enabled, the KIRQ and/or AUXOBF1 must be cleared in software.
Keyboard Command Write
This is an 8 bit write only register. When written, the C/D status bit of the status register is set to one and the IBF bit is
set.
Keyboard Status Read
This is an 8 bit read only register. Refer to the description of the Status Register for more information.
CPU-to-Host Communication
The LPC47M14x CPU can write to the Output Data register via register DBB. A write to this register automatically sets
Bit 0 (OBF) in the Status register. See Table 51.
Table 51 – Host Interface Flags
8042 INSTRUCTION
OUT DBB
FLAG
Set OBF, and, if enabled, the KIRQ output signal goes high
Host-to-CPU Communication
The host system can send both commands and data to the Input Data register. The CPU differentiates between
commands and data by reading the value of Bit 3 of the Status register. When bit 3 is "1", the CPU interprets the register
contents as a command. When bit 3 is "0", the CPU interprets the register contents as data. During a host write
operation, bit 3 is set to "1" if SA2 = 1 or reset to "0" if SA2 = 0.
KIRQ
If "EN FLAGS" has been executed and P24 is set to a one: the OBF flag is gated onto KIRQ. The KIRQ signal can be
connected to system interrupt to signify that the LPC47M14x CPU has written to the output data register via "OUT
DBB,A". If P24 is set to a zero, KIRQ is forced low. On power-up, after a valid RST pulse has been delivered to the
device, KIRQ is reset to 0. KIRQ will normally reflects the status of writes "DBB". (KIRQ is normally selected as IRQ1 for
keyboard support.)
If "EN FLAGS” has not been executed: KIRQ can be controlled by writing to P24. Writing a zero to P24 forces KIRQ
low; a high forces KIRQ high.
MIRQ
If "EN FLAGS" has been executed and P25 is set to a one:; IBF is inverted and gated onto MIRQ. The MIRQ signal can
be connected to system interrupt to signify that the LPC47M14x CPU has read the DBB register. If "EN FLAGS” has not
been executed, MIRQ is controlled by P25, Writing a zero to P25 forces MIRQ low, a high forces MIRQ high. (MIRQ is
normally selected as IRQ12 for mouse support).
SMSC DS – LPC47M14X
Page 103
Rev. 03/19/2001
SMSC [ SMSC CORPORATION ]
