LPC47M14X datasheet(76/205 Pages) SMSC

76 / 205 page

SMSC DS – LPC47M14X

Page 76

Rev. 03/19/2001

MIDI RX CLOCK

MIDI RX DATA BYTE N

MIDI RX DATA BYTE N+1

MIDI_IN

DATA READY

IRQ

nREAD

NOTE: IRQ remains asserted

until read FIFO is empty

FIGURE 4 – MPU-401 INTERRUPT

Note

DATA READY represents the Data Ready bit B0 in the 16C550A UART Line Status Register.

Note

nREAD represents host read operations from the MIDI Data register.

Note

IRQ is the MPU-401 Host Interface IRQ shown in FIGURE 3.

The 16C550A UART Receive FIFO

Threshold=1.

Note

MIDI RX CLOCK is the MIDI bit clock. The MIDI bit clock period is 32

µs.

6.8.5

MPU-401 Command Controller

Overview

Commands are written by the host to the MPU-401 MIDI Interface through the Command register (Table 34) 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 16C550A 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 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

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