15.1 Introduction
The McBSP consists of a data-flow path and a control path connected to external devices by six pins as shown
in
Data is communicated to devices interfaced with the McBSP via the data transmit (DX) pin for transmission and
via the data receive (DR) pin for reception. Control information in the form of clocking and frame synchronization
is communicated via the following pins: CLKX (transmit clock), CLKR (receive clock), FSX (transmit frame
synchronization), and FSR (receive frame synchronization).
The CPU and the DMA controller communicate with the McBSP through 16-bit-wide registers accessible via the
internal peripheral bus. The CPU or the DMA controller writes the data to be transmitted to the data transmit
registers (DXR1, DXR2). Data written to the DXRs is shifted out to DX via the transmit shift registers (XSR1,
XSR2). Similarly, receive data on the DR pin is shifted into the receive shift registers (RSR1, RSR2) and copied
into the receive buffer registers (RBR1, RBR2). The contents of the RBRs is then copied to the DRRs, which
can be read by the CPU or the DMA controller. This allows simultaneous movement of internal and external data
communications.
DRR2, RBR2, RSR2, DXR2, and XSR2 are not used (written, read, or shifted) if the serial word length is 8 bits,
12 bits, or 16 bits. For larger word lengths, these registers are needed to hold the most significant bits.
The frame and clock loop-back is implemented at chip level to enable CLKX and FSX to drive CLKR and FSR.
If the loop-back is enabled, the CLKR and FSR get their signals from the CLKX and FSX pads; instead of the
CLKR and FSR pins.
15.1.1 Features of the McBSP
The McBSP features:
• Full-duplex communication
• Double-buffered transmission and triple-buffered reception, allowing a continuous data stream
• Independent clocking and framing for reception and transmission
• The capability to send interrupts to the CPU and to send DMA events to the DMA controller
• 128 channels for transmission and reception
• Multichannel selection modes that enable or disable block transfers in each of the channels
• Direct interface to industry-standard codecs, analog interface chips (AICs), and other serially connected A/D
and D/A devices
• Support for external generation of clock signals and frame-synchronization signals
• A programmable sample rate generator for internal generation and control of clock signals and frame-
synchronization signals
• Programmable polarity for frame-synchronization pulses and clock signals
• Direct interface to:
– T1/E1 framers
– IOM-2 compliant devices
– AC97-compliant devices (the necessary multiphase frame capability is provided)
– I2S compliant devices
– SPI devices
• A wide selection of data sizes: 8, 12, 16, 20, 24, and 32 bits
Note
A value of the chosen data size is referred to as a
serial word
or
word
throughout the McBSP
documentation. Elsewhere,
word
is used to describe a 16-bit value.
• μ-law and A-law companding
• The option of transmitting/receiving 8-bit data with the LSB first
• Status bits for flagging exception/error conditions
• ABIS mode is not supported.
Multichannel Buffered Serial Port (McBSP)
878
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Summary of Contents for TMS320 2806 Series
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