SPI Port
The SPI is used as a general purpose control bus on the dspstak 21262sx. It is connected to two
onboard components, a serial flash memory and the Peripheral Microcontroller. It is also available
on the Interconnect Port to control data converters and provide general purpose I/O expansion.
Like all other dspstak DSP Engines, the DSP is always the master.
The flash memory is selected via Flag 0 of the ADSP-21262. This device is used to bootload your
application program into the internal memory of the DSP. Details on uploading programs to the
flash memory are in the Programming the dspstak 21262sx section of this manual. A special
bootloader program resides in the lowest block of the flash and is unavailable for user applications.
WARNING:
Be very careful of writing to the flash memory and never ERASE or WRITE the
lowest block of the flash! The only way to recover from an inadvertent corruption of the
bootloader program is to rewrite this space with an in-circuit emulator.
The Peripheral Microcontroller is a preprogrammed part that provides the RS-232 port, a watchdog
timer, brown out protection and user EE memory. It communicates over the SPI port using Flag 2 as
its slave select. Refer to the Peripheral Microcontroller API section of this manual for more
information.
The SPI Port is also brought out to the Interconnect Port. Flag 3 is expanded via the PLD to provide
four SPI slave select lines. Generally, the #SPI_SS pin of the Interconnect Port is used to control a
data converter on a dspstak I/O module. The additional 3 slave selects are shared with IO5, IO6
and IO7 and are usually used for expanding the SPI interface for additional I/O. For example, you
could use this interface to create a front panel on an instrument where switches or encoders were
scanned and status indicators were controlled. You could control a small LCD display via this
interface. Refer to the USB & PLD Register section of this manual for details.
Danville uses a 2x5 0.100 box header as a standard connector for SPI off-board expansion. It is
described in the dspstak Family Users Manual. We suggest you add a small (33 ohm) series resistor
at the driving end of the SPI SO line for any remote interfaces. Keep in mind that the SPI interface is
not intended for long unbuffered runs. You may need to add buffers or run the SPI interface at slow
Clock speeds for reliable operations.
dspstak™ 21262sx User Manual
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