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10.0 Musical Instrument Digital Interface (MIDI) Port (Continued)

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10.2.9

Enhanced MIDI Port Features

The MIDI Port supports the following modes/operations, which are not part of the Legacy definition of the MIDI Port:

Transmit in Pass-Thru

Loopback mode

MIDI Thru

MDTX pin masking

Transmit in Pass-Thru. When the MIDI Port is operated in Pass-Thru mode, transmit is disabled by default. To enable it,

write 1 to bit 4 of the MCNTL register.

Loopback Mode. The MIDI serial data transmit signal is routed internally to the MIDI serial data receive signal. This causes

all the data transmitted by the MIDI Port to also be received. Loopback mode can be used as a mode for testing the MIDI

Port or its software. To enable it, write 1 to bit 7 of the MCNTL register.

MIDI Thru. The MIDI serial data receive signal is routed internally to the MIDI serial data transmit signal. This causes any

incoming stream of pulses received via the MDRX pin to be driven immediately on the MDTX pin. This feature allows the

MIDI Port to be connected as a link in a chain of several MIDI devices. In parallel to routing the MIDI receive signal to the

MIDI transmit signals, the incoming serial data is also received by the MIDI Port itself. To enable it, write 1 to bit 6 of the

MCNTL register.

MDTX Pin Masking. MDTX pin masking forces this pin to remain at a high level. This causes all transmit processes to occur

without physically driving the serial data via the MDTX pin. Writing 1 to bit 2 of the MCNTL register enables MDTX pin mask-

ing.

The above three features are handled by the MIDI Signals Routing Control Logic, which is illustrated in Figure 34..

Figure 34. MIDI Signals Routing Control Logic

MDTX Pin

MDRX Pin

MIDI

Transmit

Signal

MIDI

Receive

Signal

Loopback

Mode

Enable

MIDI Thru

Enable

MDTX Pin

Masking

Enable

PC87366 Datenblatt(PDF) 172 Page - National Semiconductor (TI)