
UART MODE Command 
The UART MODE command is 3Fh. The UART MODE command clears the 16C550A transmit and receive FIFOs, 
places the command acknowledge byte (FEh) in the MIDI Data port receive buffer, and enables the 16C550A UART 
for transmit and receive operations.   
In UART mode, the MPU-401 Interface passes MIDI read and write data directly between the host (using the MIDI 
Data port) and the 16C550A UART Transmit and Receive buffers. 
The MPU-401 Command Controller ignores the UART MODE command when the MPU-401 Interface is already in 
UART mode. 
The MPU-401 RESET command is executed but not acknowledged by the MPU-401 Command Controller in UART 
MODE (see Section “RESET Command”, above). 
Command Acknowledge Byte 
Under certain conditions, the command controller acknowledges the RESET and UART MODE commands with a 
command acknowledge byte (FEh). 
The command acknowledge byte appears as read-data in the MIDI Data port. 
Note
: 
The command acknowledge byte will appear as the next available data byte in the receive buffer of the MIDI 
Data port.  For example if the receive FIFO is not empty when an MPU-401 RESET command is received, the 
command acknowledge will appear first, before any unread FIFO data.  In the examples above, the receive FIFO is 
cleared before the command acknowledge byte is placed in the MIDI Data port read buffer. 
7.7.6 MIDI UART 
Overview 
The UART is used to transmit and receive MIDI protocol data from the MIDI Data port in the Host Interface (see 
Section “Host Interface”). 
The MIDI protocol requires 31.25k Baud (
±
1%) and 10 bits total per frame: 1 start bit, 8 data bits, no parity, and 1 
stop bit.  For example, there are 320 microseconds per serial MIDI data byte.  MIDI data is transferred LSB first 
(Figure 7). 
The UART is configured in full-duplex mode for the MPU-401 MIDI Interface, with 16-byte send/receive FIFOs.  
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MIDI RX CLOCK
1
MIDI RX DATA BYTE (01H)
MIDI_IN
FIGURE 4 - MIDI DATA BYTE EXAMPLE 
Note
1
7.7.7 MPU-401 CONFIGURATION REGISTERS 
The LPC47M192 configuration registers are in Logical Device B (see “Configuration” section).  The configuration 
registers contain the MPU-401 Activate, Base Address and Interrupt select.  The defaults for the Base Address and 
Interrupt Select configuration registers match the MPU-401 factory defaults. 
MIDI RX CLOCK is the MIDI bit clock.  The MIDI bit clock period is 32
μ
s.