Digilent Nexys 3 Reference Manual page 9

Nexys 3™ FPGA Board Reference Manual
port for serial data transfer, but that function is not enabled on the Nexys 3 board (the ADV and WAIT signals are
connected between the FPGA and PCM, but they serve no functions).
The Cellular RAM and parallel PCM share a common 16-bit data bus and 24-bit address bus. The Cellular RAM is
byte addressable using the upper-byte and lower-byte signals (MT-UB and MT-LB), but the P8P PCM is configured
for 16 byte operations only (it is not byte addressable). The output enable (OE) and write enable (WE) signals are
shared by both devices, but each device has individual chip enable (CE) signals. Additionally, the Cellular RAM has
clock (MT-CLK), wait (MT-WAIT), address valid (MT-ADV) and control register enable (MT_CRE) signals available to
the FPGA for use with synchronous transfers, and the PCM device has Reset (RP#). With simple changes, the Nexys
3 board can accommodate either the PCM device or the older "P33" Flash device. The signal names in the Nexys 3
schematic reference the P33 device; the P33 ADV and WAIT signals are not used in by the PCM device.
The 16Mbyte serial PCM device (Micron part number NP5Q128A13ESFC0E) is also bit alterable without requiring
an erase cycle. It supports the legacy SPI protocol as well as the newer Quad I/O and Dual I/O protocols, at bus
speeds up to 50MHz.
FPGA configuration files can be written to both PCM devices, and mode settings are available to cause the FPGA to
automatically read a configuration from one of these devices at power on. A Spartan-6 LX16 configuration file
requires about 512Kbytes of memory, leaving about 97% of the PCM devices available for user data.
Both PCM devices are loaded with configuration files at the factory. The SPI PCM device contains a file that
configures the FPGA to test the Nexys 3 memory devices during manufacturing, and this file isn't needed after the
board test is complete. The BPI PCM device contains a file that configures the Nexys 3 with a basic user
demonstration program, and it can be used to verify board functions. This same .bit file is available for download
from the Digilent website. If Mode jumper J8 is set to BPI mode and power is applied, the user demo configuration
will be loaded. The demo drives a counter on the 7-segment display, drives the user LEDs on and off when the user
switches are toggled, turns off digits on the 7-segment display when user buttons are pressed, and drives an image
out the VGA port. A USB mouse can be connected to J4 for a simple visual demonstration.
Please refer to the manufacturer's data sheets and the reference designs posted on Digilent's website for more
information about the memory devices.
Copyright Digilent, Inc. All rights reserved.
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