LPC47M192 datasheet(81/228 Pages) SMSC

81 / 228 page

SMSC DS – LPC47M192

Page 81

Rev. 03/30/05

DATASHEET

Interrupt

The MPU-401 IRQ is asserted (‘1’) when either MIDI receive data or a command acknowledge byte is available tot he

host in the MIDI data register (FIGURE 3). the IRQ is deasserted (‘0’) when the host reads the MIDI Data port.

Note: If, following a host read, data is still available in the 16C550A Receive FIFO, the IRQ will remain asserted (‘1’).

The IRQ is enabled when the ‘Activate’ bit in the MPU-401 configuration registers logical device block is asserted ‘1’.

If the Activate bit is deasserted ‘0’, the MPU-401 IRQ cannot be asserted (see Section “MPU-401 Configuration

Registers”).

The MPU-401 IRQ is not affected by MIDI write data, 16C550A transmit-related functions or Receiver Line Status

interrupts.

The factory default Sound Blaster 16 MPU-401 IRQ is 5.

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 3 - MPU-401 INTERRUPT

NOTE1 DATA READY represents the Data Ready bit B0 in the 16C550A UART Line Status Register.

NOTE2 nREAD represents host read operations from the MIDI Data register.

NOTE3 IRQ is the MPU-401 Host Interface IRQ shown in FIGURE 2. The 16C550A UART Receive FIFO

Threshold=1.

NOTE4 MIDI RX CLOCK is the MIDI bit clock. The MIDI bit clock period is 32

µs.

7.7.5 MPU-401 COMMAND CONTROLLER

Overview

Commands are written by the host to the MPU-401 MIDI Interface through the Command register (Table 33) and are

immediately interpreted by the MPU-401 Command Controller shown in FIGURE 2. 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.

LPC47M192 Datasheet(PDF) 81 Page - SMSC Corporation

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