ADSP-21367/ADSP-21368/ADSP-21369
Serial ports operate in five modes:
• Standard DSP serial mode
• Multichannel (TDM) mode with support for packed I2S
mode
• I2S mode
• Packed I2S mode
Digital Peripheral Interface (DPI)
The digital peripheral interface provides connections to two
serial peripheral interface ports (SPI), two universal asynchro-
nous receiver-transmitters (UARTs), a two-wire interface
(TWI), 12 flags, and three general-purpose timers.
Serial Peripheral (Compatible) Interface
The processors contain two serial peripheral interface ports
(SPIs). The SPI is an industry-standard synchronous serial link,
enabling the SPI-compatible port to communicate with other
SPI-compatible devices. The SPI consists of two data pins, one
device select pin, and one clock pin. It is a full-duplex synchro-
nous serial interface, supporting both master and slave modes.
The SPI port can operate in a multimaster environment by
interfacing with up to four other SPI-compatible devices, either
acting as a master or slave device. The ADSP-21367/
ADSP-21368/ADSP-21369 SPI-compatible peripheral imple-
mentation also features programmable baud rate and clock
phase and polarities. The SPI-compatible port uses open drain
drivers to support a multimaster configuration and to avoid
data contention.
• Left-justified sample pair mode
Left-justified sample pair mode is a mode where in each frame
sync cycle two samples of data are transmitted/received—one
sample on the high segment of the frame sync, the other on the
low segment of the frame sync. Programs have control over var-
ious attributes of this mode.
Each of the serial ports supports the left-justified sample pair
and I2S protocols (I2S is an industry-standard interface com-
monly used by audio codecs, ADCs, and DACs such as the
Analog Devices AD183x family), with two data pins, allowing
four left-justified sample pair or I2S channels (using two stereo
devices) per serial port, with a maximum of up to 32 I2S chan-
nels. The serial ports permit little-endian or big-endian
transmission formats and word lengths selectable from 3 bits to
32 bits. For the left-justified sample pair and I2S modes, data-
word lengths are selectable between 8 bits and 32 bits. Serial
ports offer selectable synchronization and transmit modes as
well as optional μ-law or A-law companding selection on a per
channel basis. Serial port clocks and frame syncs can be inter-
nally or externally generated.
UART Port
The processors provide a full-duplex universal asynchronous
receiver/transmitter (UART) port, which is fully compatible
with PC-standard UARTs. The UART port provides a simpli-
fied UART interface to other peripherals or hosts, supporting
full-duplex, DMA-supported, asynchronous transfers of serial
data. The UART also has multiprocessor communication capa-
bility using 9-bit address detection. This allows it to be used in
multidrop networks through the RS-485 data interface stan-
dard. The UART port also includes support for five data bits to
eight data bits, one stop bit or two stop bits, and none, even, or
odd parity. The UART port supports two modes of operation:
The serial ports also contain frame sync error detection logic
where the serial ports detect frame syncs that arrive early (for
example, frame syncs that arrive while the transmission/recep-
tion of the previous word is occurring). All the serial ports also
share one dedicated error interrupt.
S/PDIF-Compatible Digital Audio Receiver/Transmitter
and Synchronous/Asynchronous Sample Rate Converter
• PIO (programmed I/O) – The processor sends or receives
data by writing or reading I/O-mapped UART registers.
The data is double-buffered on both transmit and receive.
The S/PDIF receiver/transmitter has no separate DMA chan-
nels. It receives audio data in serial format and converts it into a
biphase encoded signal. The serial data input to the
• DMA (direct memory access) – The DMA controller trans-
fers both transmit and receive data. This reduces the
number and frequency of interrupts required to transfer
data to and from memory. The UART has two dedicated
DMA channels, one for transmit and one for receive. These
DMA channels have lower default priority than most DMA
channels because of their relatively low service rates.
receiver/transmitter can be formatted as left-justified, I2S, or
right-justified with word widths of 16, 18, 20, or 24 bits.
The serial data, clock, and frame sync inputs to the S/PDIF
receiver/transmitter are routed through the signal routing unit
(SRU). They can come from a variety of sources such as the
SPORTs, external pins, the precision clock generators (PCGs),
or the sample rate converters (SRC) and are controlled by the
SRU control registers.
The UART port’s baud rate, serial data format, error code gen-
eration and status, and interrupts are programmable:
• Supporting bit rates ranging from (fSCLK/ 1,048,576) to
(fSCLK/16) bits per second.
The sample rate converter (SRC) contains four SRC blocks and
is the same core as that used in the AD1896 192 kHz stereo
asynchronous sample rate converter and provides up to 128 dB
SNR. The SRC block is used to perform synchronous or asyn-
chronous sample rate conversion across independent stereo
channels, without using internal processor resources. The four
SRC blocks can also be configured to operate together to con-
vert multichannel audio data without phase mismatches.
Finally, the SRC can be used to clean up audio data from jittery
clock sources such as the S/PDIF receiver.
• Supporting data formats from 7 bits to 12 bits per frame.
• Both transmit and receive operations can be configured to
generate maskable interrupts to the processor.
Where the 16-bit UART_Divisor comes from the DLH register
(most significant eight bits) and DLL register (least significant
eight bits).
Rev. A
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Page 8 of 56
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August 2006
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