PC87373 datasheet(134/174 Pages) NSC

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

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The Receive FIFO Full and Transmit FIFO Empty status flags are reflected by MSTAT register bits 5 and 2, respectively.

These bits are updated only when the MIDI Port operates in UART mode or when in Pass-Thru mode with the Receive FIFO

enabled. Otherwise, these bits are constantly cleared. The values of these bits are set by the MIDI Port hardware and are

not affected by reading the MSTAT register.

The Receive Overrun Error flag indicates that serial data was received by the MIDI Communication Engine while the Receive

Buffer of FIFO was full. This flag is reflected by bit 3 of the MSTAT register. It is updated in both Pass-Thru and UART modes.

When a Receive Overrun Event occurs, the data in the Receive Buffer/FIFO is kept and all incoming data is lost. Incoming

data will keep getting lost until there is room in the Receive Buffer/FIFO to accept it. The Receive Overrun Error status flag

is cleared when the MSTAT register is read.

The MIDI Port Operation Mode flag indicates whether the MIDI Port is currently operating in Pass-Thru or UART mode. This

status flag is reflected by bit 4 of the MSTAT register. It can be used by software to keep track of the currently selected MIDI

Port operation mode.

11.2.8 MIDI Port Interrupts

The MIDI Port supports interrupt assertion in both Pass-Thru and UART modes in response to one or both of the following

events:

Receive Data Ready

Transmit Buffer Empty

The Receive Data Ready event refers to the case in which there is data to be read in the Receive Buffer/FIFO. An interrupt

request is asserted by the MIDI Port to indicate a Receive Data Ready event in one of the following cases:

• The MIDI Port is in Pass-Thru mode and the Receive Buffer contains a data or acknowledge byte that has not been read

yet. In this case, the interrupt request is de-asserted once the Receive buffer is read.

• The MIDI Port is either in UART mode and the Receive FIFO contains eight or more data bytes that have not been read

yet, or it is in Pass-Thru mode with the Receive FIFO enabled. In this case, the interrupt request is de-asserted once the

Receive FIFO level drops below eight bytes.

• The MIDI Port is in UART mode, the Receive FIFO contains less than eight data bytes which have not been read yet,

and no data was received by the Communication Engine, the MIDI Port is in Pass-Thru mode with the Receive FIFO

enabled, or a read occurs from the Receive FIFO during a timeout period of approximately 1.28 msec (the time it takes

to transfer 4 bytes over the MIDI communication channel). In this case, the interrupt request is de-asserted when either

new data is received by the Communication Engine or data is read from the Receive FIFO.

The Transmit Buffer Empty event refers to the case in which the Transmit Buffer/FIFO of the MIDI Port can still accept data

to transmit. An interrupt request is asserted by the MIDI Port to indicate a Transmit Buffer Empty event in one of the following

cases:

• The MIDI Port is in Pass-Thru mode and the Transmit Buffer is empty. In this case, the interrupt request is de-asserted

once a byte is written to the Transmit Buffer.

• The MIDI Port is in UART mode and the Transmit FIFO is empty. In this case, the interrupt request is de-asserted once

the Transmit FIFO is filled with at least three bytes.

After a Hardware reset, interrupts are asserted by the MIDI Port only in response to a Receive Data Ready event. Interrupt

assertion in response to Transmit Buffer Empty events can be enabled by writing 1 to bit 1 of the MCNTL register. Interrupt

assertion in response to Receive Data Ready events can be disabled by writing 0 to bit 3 of the MCNTL register.

11.2.9 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 caus-

es 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.

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