Functional Overview
3.8 Multichannel Buffered Serial Ports (McBSPs)
The 5407/5404 device provides three high-speed, full-duplex, multichannel buffered serial ports that allow
direct interface to other C54x/LC54x devices, codecs, and other devices in a system. The McBSPs are based
on the standard serial-port interface found on other 54x devices. Like their predecessors, the McBSPs provide:
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Full-duplex communication
Double-buffer data registers, which allow a continuous data stream
Independent framing and clocking for receive and transmit
In addition, the McBSPs have the following capabilities:
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Direct interface to:
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T1/E1 framers
MVIP switching compatible and ST-BUS compliant devices
IOM-2 compliant devices
AC97-compliant devices
IIS-compliant devices
Serial peripheral interface
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Multichannel transmit and receive of up to 128 channels
A wide selection of data sizes, including 8, 12, 16, 20, 24, or 32 bits
µ-law and A-law companding
Programmable polarity for both frame synchronization and data clocks
Programmable internal clock and frame generation
The McBSP consists of a data path and control path. The six pins, BDX, BDR, BFSX, BFSR, BCLKX, and
BCLKR, connect the control and data paths to external devices. The implemented pins can be programmed
as general-purpose I/O pins if they are not used for serial communication. Note that on McBSP2, the transmit
and receive clocks and the transmit and receive frame sync have been combined.
The data is communicated to devices interfacing to the McBSP by way of the data transmit (BDX) pin for
transmit and the data receive (BDR) pin for receive. The CPU or DMA reads the received data from the data
receive register (DRR) and writes the data to be transmitted to the data transmit register (DXR). Data written
to the DXR is shifted out to BDX by way of the transmit shift register (XSR). Similarly, receive data on the BDR
pin is shifted into the receive shift register (RSR) and copied into the receive buffer register (RBR). RBR is then
copied to DRR, which can be read by the CPU or DMA. This allows internal data movement and external data
communications simultaneously.
Control information in the form of clocking and frame synchronization is communicated by way of BCLKX,
BCLKR, BFSX, and BFSR. The device communicates to the McBSP by way of 16-bit-wide control registers
accessible via the internal peripheral bus.
The control block consists of internal clock generation, frame synchronization signal generation, and their
control, and multichannel selection. This control block sends notification of important events to the CPU and
DMA by way of two interrupt signals, XINT and RINT, and two event signals, XEVT and REVT.
The on-chip companding hardware allows compression and expansion of data in either µ-law or A-law format.
When companding is used, transmitted data is encoded according to the specified companding law and
received data is decoded to 2s complement format.
The sample rate generator provides the McBSP with several means of selecting clocking and framing for both
the receiver and transmitter. Both the receiver and transmitter can select clocking and framing independently.
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SPRS007D
November 2001 − Revised April 2004
TI [ TEXAS INSTRUMENTS ]
