CS4239 Datasheet, PDF (63/98 Pages) Cirrus Logic – CrystalClear™ Portable ISA Audio System

CS4239
CrystalClear^TM Portable ISA Audio System
MPU-401 INTERFACE
The MPU-401 is an intelligent MIDI interface
that was introduced by Roland in 1984. Voyetra
Technologies subsequently introduced an IBM-
PC plug in card that incorporated the MPU-401
functionality. The MPU-401 has become the de-
facto standard for controlling MIDI devices via
IBM-PC compatible personal computers.
Although the MPU-401 does have some intelli-
gence, a non-intelligent mode is available in
which the MPU-401 operates as a basic UART.
By incorporating hardware to emulate the MPU-
401 in UART mode, MIDI capability is
supported.
MPU-401 Register Interface
The MPU401 logical device software interface
occupies 2 I/O locations, utilizes 10-bit address
decoding, and is located at PnP address
’MPUbase’. 10-bit addressing requires that the
upper address bits be 0 to decode a valid ad-
dress, i.e. no aliasing occurs. The standard base
address is 330h. This device also uses an inter-
rupt, typically 9.
MPUbase+0 is the MIDI Transmit/Receive port
and MPUbase+1 is the Command/Status port. In
addition to I/O decodes the only additional func-
tionality required from an ISA bus viewpoint is
the generation of a hardware interrupt whenever
data has been received into the receive buffer.
MIDI Transmit/Receive Port,
MPUbase+0
D7 D6 D5 D4 D3 D2 D1 D0
TR7 TR6 TR5 TR4 TR3 TR2 TR1 TR0
TR7-TR0
The MIDI Transmit/Receive Port is
used to send and receive MIDI data
as well as status information that
was returned from a previously sent
command.
All MIDI transmit data is transferred through a
16-byte FIFO and receive data through a 16-byte
FIFO. The FIFO gives the ISA interface time to
respond to the asynchronous MIDI transfer rate
of 31.25 k baud.
The Command/Status Registers occupy the same
address and are used to send instructions to and
receive status information from the MPU-401.
Command Register, write only
MPUbase+1
D7 D6 D5 D4 D3 D2 D1 D0
CS7 CS6 CS5 CS4 CS3 CS2 CS1 CS0
CS7-CS0
Each write to the Command/Status
Register produces an appropriate
acknowledge byte in the receive reg-
ister.
Status Register, read only
MPUbase+1
D7 D6 D5 D4 D3 D2 D1 D0
RXS TXS CS5 CS4 CS3 CS2 CS1 CS0
CS5-CS1
TXS
RXS
D0-D5 are the 6 LSBs of the last
command written to this port.
Transmit Buffer Status Flag.
0 - Transmit buffer not full
1 - Transmit buffer full
Receive Buffer Status Flag
0 - Data in Receive buffer
1 - Receive buffer empty
When in "UART" mode, data is received into the
receive buffer FIFO and a hardware interrupt is
generated. Data can be received from two
sources: MIDI data via the UART serial input or
acknowledge data that is the result of a write to
the Command Register (MPUbase+1). The inter-
rupt is cleared by a read of the MIDI Receive
Port (MPUbase+0).
DS253PP2
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