Registers (Ports)
The run-time registers in the MPU-401 Host Interface are shown below in Table 34.
Table 34 – MPU-401 Host Interface Registers
REGISTER NAME
ADDRESS
TYPE
DESCRIPTION
MIDI DATA
MPU-401 I/O Base Address
R/W
Used for MIDI transmit data, MIDI
receive data, and MPU-401 command
acknowledge.
STATUS
MPU-401 I/O Base Address + 1
MPU-401 I/O Base Address + 1
R
Used to indicate the send/receive status
of the MIDI Data port.
Used for MPU-401 Commands.
COMMAND
W
6.8.3
MIDI Data Port
The MIDI Data port exchanges MIDI transmit and MIDI receive data between the MPU-401 UART interface and the
host. The MIDI Data port is read/write (Table 35). The MIDI Data port is also used to return the command
acknowledge byte ‘FEh’ following host writes to the COMMAND port.
The MIDI Data port is full-duplex; i.e., the transmit and receive buffers can be used simultaneously.
An interrupt is generated when either MIDI receive data or a command acknowledge is available to the host in the
MIDI Data register. See Section “Bit 7 – MIDI Receive Buffer Empty” and “Interrupt”
Table 35 – MIDI Data Port
MPU-401 I/O BASE ADDRESS
D7
D6
D5
D4
D3
D2
D1
D0
DEFAULT
TYPE
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
n/a
NAME
MIDI DATA/COMMAND-ACKNOWLEDGE REGISTER
6.8.4
Status Port
The Status port is used to indicate the state of the transmit and receive buffers in the MIDI Data port. The Status port
is read-only (Table 36). Status port Bit 6 is MIDI Transmit Busy, Bit 7 is MIDI Receive Buffer Empty. The remaining
bits in the Status port are RESERVED.
Table 36 – MPU-401 Status Port
MPU-401 I/O BASE ADDRESS+1
D7
R
D6
R
D5
R
D4
R
D3
R
D2
R
D1
R
D0
R
DEFAULT
TYPE
BIT
0x80
MIDI RX MIDI TX
0
0
0
0
0
0
NAME
BUFFE
R
BUSY
EMPTY
Bit 7 – MIDI Receive Buffer Empty
Bit 7 MIDI Receive Buffer Empty indicates the read state of the MIDI Data port (Table 37). If the MRBE bit is ‘0’, MIDI
Read/Command Acknowledge data is available to the host. If the MRBE bit is ‘1’, MIDI Read/Command
Acknowledge data is NOT available to the host.
The MPU-401 Interrupt output is active ‘1’ when the MIDI Receive Buffer Empty bit is ‘0’. The MPU-401 Interrupt
output is inactive ‘0’ when the MIDI Receive Buffer Empty bit is ‘1’. See Section “Interrupt” for more information.
SMSC DS – LPC47M14X
Page 74
Rev. 03/19/2001
SMSC [ SMSC CORPORATION ]
