Spectrum Digital, Inc
2-7
2.3 Synchronous DRAM
The DSK uses a 128 megabit synchronous DRAM (SDRAM) on the 32-bit EMIF. The
SDRAM is mapped at the beginning of CE0 (address 0x80000000). Total available
memory is 16 megabytes. The integrated SDRAM controller is part of the EMIF and
must be configured in software for proper operation. The EMIF clock is derived from the
PLL settings and should be configured in software at 90MHz. This number is based on
an internal PLL clock of 450MHz required to achieve 225 MHz operation with a divisor
of 2 and a 90MHz EMIF clock with a divisor of 5.
When using SDRAM, the controller must be set up to refresh one row of the memory
array every 15.6 microseconds to maintain data integrity. With a 90MHz EMIF clock,
this period is 1400 bus cycles.
2.4 Flash Memory
Flash is a type of memory which does not lose its contents when the power is turned
off. When read it looks like a simple asynchronous read-only memory (ROM). Flash
can be erased in large blocks commonly referred to as sectors or pages. Once a block
has been erased each word can be programmed once through a special command
sequence. After than the entire block must be erased again to change the contents.
The DSK uses a 512Kbyte external Flash as a boot option. It is visible at the beginning
of CE1 (address 0x90000000). The Flash is wired as a 256K by 16 bit device to support
the DSK's 16-bit boot option. However, the software that ships with the DSK treats the
Flash as an 8-bit device (ignoring the top 8 bits) to match the 6713's default 8-bit boot
mode. In this configuration, only 256Kbytes are readily usable without software
changes.
2.5 LEDs and DIP Switches
The DSK includes 4 software accessible LEDs (D7-D10) and DIP switches (SW1) that
provide the user a simple form of input/output. Both are accessed through the CPLD
USER_REG register.
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