
SMSC DS – LPC47M14X 
Page 74 
Rev. 03/19/2001 
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
MIDI DATA 
ADDRESS
TYPE
R/W 
DESCRIPTION
MPU-401 I/O Base Address 
Used for MIDI transmit data, MIDI 
receive data, and MPU-401 command 
acknowledge. 
Used to indicate the send/receive status 
of the MIDI Data port. 
Used for MPU-401 Commands.  
STATUS  
MPU-401 I/O Base Address + 1 
R 
COMMAND 
MPU-401 I/O Base Address + 1 
W 
6.8.3 
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”  
MIDI Data Port 
Table 35  –  MIDI Data Port 
MPU-401 I/O BASE ADDRESS
D4
R/W
TYPE
NAME
D7
R/W
MIDI DATA/COMMAND-ACKNOWLEDGE REGISTER 
D6
R/W
D5
R/W
D3
R/W
D2
R/W
D1
R/W
D0
R/W
DEFAULT
n/a 
6.8.4 
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. 
Status Port 
Table 36  –  MPU-401 Status Port 
MPU-401 I/O BASE ADDRESS+1
D4
R 
0 
0 
TYPE 
BIT 
NAME 
D7
R 
MIDI RX 
BUFFE
R 
EMPTY 
D6
R 
MIDI TX 
BUSY 
D5
R 
D3
R 
D2
R 
D1
R 
D0
R 
DEFAULT
0x80 
0 
0 
0 
0 
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.