LPC47M112 datasheet(82/208 Pages) SMSC

82 / 208 page

Enhanced Super I/O Controller with LPC Interface

Datasheet

SMSC DS – LPC47M112

Page 82

Rev. 02/02/2005

17.1

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.

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