Analog Devices ADSP-21261 SHARC Hardware Reference Manual page 52

Architectural Overview
transmit modes. Serial port clocks and frame syncs can be internally or
externally generated.
Parallel Port. The ADSP-2126x parallel port provides the processor inter-
face to asynchronous 8-bit memory. The parallel port supports a 66M
bytes per second transfer rate and 256 word page boundaries. The on-chip
DMA controller automatically packs external data into the appropriate
word width during transfers.
The parallel port supports packing of 32-bit words into 8-bit or 16-bit
external memory and programmable external data access duration from 3
to 32 clock cycles.
Serial Peripheral (Compatible) Interface (SPI). The ADSP-2126x SPI is
an industry standard synchronous serial link that enables the SPI-compat-
ible port to communicate with other SPI-compatible devices. SPI is an
interface consisting of two data pins, one device select pin, and one clock
pin. It is a full-duplex synchronous serial interface, supporting both mas-
ter and slave modes. It can operate in a multi master environment by
interfacing with up to four other SPI-compatible devices, either acting as a
master or slave device.
The SPI-compatible peripheral implementation also supports programma-
ble baud rate and clock phase/polarities, as well as the use of open drain
drivers to support the multi master scenario to avoid data contention.
ROM Based Security. For ADSP-2126x processors with application code
in the on-chip ROM, an optional ROM security feature is included. This
feature provides hardware support for securing user software code by pre-
venting unauthorized reading from the enabled code. The processor does
not boot-load any external code, executing exclusively from internal
ROM. The processor also is not freely accessible via the JTAG port.
Instead, a 64-bit key is assigned to the user. This key must be scanned in
through the JTAG or Test Access Port. The device ignores a wrong key.
Emulation features and external boot modes are only available after the
correct key is scanned.
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