PC87363 Datasheet, PDF (165/200 Pages) National Semiconductor (TI) – 128-Pin LPC SuperI/O with MIDI and Game Ports, Extended Wake-Up and Protection

10.0 Musical Instrument Digital Interface (MIDI) Port (Continued)
UART Mode
Entering UART mode is done by software, by giving the MIDI Port command of 3Fh. Once in UART mode, both transmit and
receive are enabled. In addition, the two 16-byte Receive and Transmit FIFOs are automatically enabled.
In UART mode, data written to the MDO register is placed in the Transmit FIFO, from which it is taken by the MIDI Commu-
nication Engine and transmitted via the MDTX pin to the MIDI device. Likewise, whenever the Transmit FIFO is not empty,
the next byte is taken out by the Communication Engine and transmitted via the MDTX pin to the MIDI device.
Whenever serial data is received by the Communication Engine via the MDRX pin, it is de-serialized and put in the Receive
FIFO. Reading the MDI register returns the next byte in the Receive FIFO. The MDI register should not be read while the
Receive FIFO is empty. If serial data is received while the Receive FIFO is full, this data is lost and not stored in the Receive
FIFO, thus keeping the data that was previously stored in the Receive FIFO.
When in UART mode, the MIDI Port responds to commands given by the host as follows:
q _{A command of FFh returns the MIDI Port to Pass-Thru mode, and resets it to its initial state.}
q _{All other commands, issued while the MIDI Port is in UART mode, are ignored.}
When switching from UART mode to Pass-Thru mode, any data previously stored in the Receive FIFO is lost, unless the
FIFO is enabled for Pass-Thru mode.
As in Pass-Thru mode, if a command is issued to the MIDI Port while the MIDI Communication Engine is in the middle of a
byte transfer, the execution of the command and the response are postponed until the ongoing byte transfer is completed.
The MIDI commands supported by the MIDI Port and their respective responses are listed in Table 47.
After each MIDI Port operation in UART mode, the MSTAT register is updated accordingly.
Table 47. MIDI Commands Supported by the MIDI Port
Command
3Fh
A0h-A7h, ABh
ACh
ADh
AFh
FFh
Others
MIDI Port Response
Pass-Thru Mode
UART Mode
Enter UART mode
FEh (Acknowledge)
Ignored
FEh (Acknowledge)
00h
Ignored
FEh (Acknowledge)
15h
Ignored
FEh (Acknowledge)
01h
Ignored
FEh (Acknowledge)
64h
Ignored
MIDI Port Reset
FEh (Acknowledge)
Enter Pass-Thru Mode
MIDI Port Reset
FEh (Acknowledge)
Ignored
10.2.7 MIDI Port Status Flags
The status of the various functional units of the MIDI Port is reflected by the MSTAT register. This register is functional in
both Pass-Thru and UART modes. Some of the status indications provided by the MSTAT register are not included in the
Legacy definition of the MIDI Port. These indications can be ignored, if not required by the software.
The following status flags are included in the Legacy definition of the MIDI Port:
q _{Receive Buffer Empty}
q _{Transmit Buffer Full}
The Receive Buffer Empty flag is reflected by bit 7 of the MSTAT register. The Transmit Buffer Full flag is reflected by bit 6
of the MSTAT register. When operating in UART mode, these bits reflect the status of the Receive and Transmit FIFOs.
The Receive Buffer Empty status flag is cleared to 0 also when an acknowledge byte is put by the MIDI Port itself following
a MIDI command.
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