NOTE3 IRQ is the MPU-401 Host Interface IRQ shown in Figure 2. The UART Receive FIFO
Threshold = 1.
NOTE4 MIDI RX CLOCK is the MIDI bit clock. The MIDI bit clock period is 32µs.
MPU-401 Command Controller
Overview
Commands are written by the host to the MPU-401 MIDI Interface through the Command register
(Table 38) and are immediately interpreted by the MPU-401 Command Controller shown in Figure 3.
The MPU-401 Command Controller in this implementation only responds to the MPU-401 RESET (FFh)
and UART MODE (3Fh) commands. All other commands are ignored.
Under certain conditions, the Command Controller acknowledges MPU-401 commands with a
command acknowledge byte (FEh).
RESET Command
The RESET command is FFh. The RESET command resets the MPU-401 MIDI Interface. Reset
disables the MPU-401 UART MODE command, disables the UART, clears the receive FIFO. The
command controller places the command acknowledge byte ‘FEh’ in the MIDI Data port read buffer if
the interface is not in the UART mode.
The RESET command is executed but not acknowledged when the command is received while the
interface is in the UART mode.
When the MPU-401 is reset, receive data from the MIDI_IN port as well as data written by the host to
the MIDI Data port is ignored.
The MPU-401 MIDI Interface is reset following the RESET command or POR.
UART MODE Command
The UART MODE command is 3Fh. The UART MODE command clears the transmit and receive
FIFOs, places the command acknowledge byte (FEh) in the MIDI Data port receive buffer, and enables
the 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 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.
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”).
SMSC LPC47B27x
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Rev. 08-10-04
DATASHEET
SMSC [ SMSC CORPORATION ]
