PC87373 datasheet(131/174 Pages) NSC

131 / 174 page

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

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Revision 1.1

Figure 39. MIDI Port Block Diagram

11.2.1 Internal Bus Interface Unit

The Internal Bus Interface Unit handles all read and write transactions between the host and the registers of the MIDI Port.

It also controls the MIDI Port interrupt request logic (see Section 11.2.8).

11.2.2 Port Control and Status Registers

A Control register (MCNTL; see Section 11.3.6 on page 138) and a Status register (MSTAT; see Section 11.3.4 on

page 137) allow the user to control the operation of the MIDI, and provide status information regarding its various functional

units. A Command register (MCOM; see Section 11.3.5 on page 138) allows the user to control the operation mode of the

MIDI Port by serving as a port via which the host can issue commands to the MIDI. A MIDI Port command is defined as a

write access to the MIDI Command register. The meaning of each command is determined by the data byte written during

this write access.

11.2.3 Data Buffers and FIFOs

The Data Buffers and FIFOs function as a mechanism for synchronizing between the Internal Bus Interface Unit and the

MIDI Communication Engine. This synchronization allows each of these units to handle its own tasks without having to

pause to send/receive data to/from the other unit. Synchronization also bridges the gap in the data transfer rate between

these two units. Data transfer rate matching is done when the FIFOs of the MIDI Port are enabled. It allows the MIDI Port to

interface a bus at a relatively high data transfer rate while maintaining communication with a MIDI device over a communi-

cation channel that supports a relatively low data transfer rate.

11.2.4 MIDI Communication Engine

The MIDI Communication Engine handles the serializing of outgoing data and the de-serializing of incoming data transferred

between the MIDI Port and the MIDI device. During Transmit (serial data transfer from the MIDI Port to the MIDI device), the

Communication Engine receives data bytes from the output data buffer or FIFO, serializes them into a stream of data bits,

and transmits them as a sequence of high and low pulses over the MDTX pin according to the MIDI communication protocol.

During Receive (serial data transfer from the MIDI device to the MIDI Port), the Communication Engine receives a sequence

of high and low pulses via the MDRX pin, converts them into a stream of data bits and de-serializes them into data bytes

that it sends to the input data buffer or FIFO.

Both Transmit and Receive are performed at a fixed serial data rate of 31.25 Kbits per second. The serial data format is also

fixed, and consists of 1 Start bit, 8 Data bits and 1 Stop bit. See the waveform illustrating a MIDI byte transfer in Figure 40.

Figure 40. MIDI Byte Transfer Waveform

Internal

Interface

MIDI

Routing

Control

Signals

MIDI

Communication

Engine

Data

Buffers

and

FIFOs

MDTX Pin

MDRX Pin

MIDI

Transmit

Signal

MIDI

Receive

Signal

(Data Serializer)

Bus

Control

Tx Data

Rx Data

SuperI/O

Internal

Bus

MIDI Port

Control and Status

Registers

Read/Write

Interface

Routing

Control

Data Buffer

Status and Control

Communication

Status and Control

Asynchronous

Synchronous

Interface

Unit

Control

Tx Data

Rx Data

MIDI Signal

Data Bits

Start

Bit

Stop

Bit

µsec

LSB

MSB

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