Xilinx Decimal Counter

CS 240

50 points, due May 7, 2008

In this assignment you'll be implementing a decimal up/down counter in VHDL and using the Xilinx boards to test your design.

Input Signals

1. 100 MHz clock. The clock signal arrives at the FPGA on pin P88.

2. !Reset. The reset signal arrives at the FPGA on pin P50 (The D0 pin of the parallel port).

3. Hold. The hold signal arrives at the FPGA on pin P48 (The D1 pin of the parallel port).

4. Up/!Down. The up/!down signal arrives at the FPGA on pin P42 (The D2 pin of the parallel port).

Output Signals

1. Output a logic '1' on P41. This will disable the FLASH from driving the data bus it shares with the seven segment display.

2. This figure shows the mapping between seven segment display segments and FPGA pins:
   

Circuit Operation

1. When !reset is brought low, the count should reset to 0. This signal has highest priority.

2. When hold is brought high, the current count should be held.

3. When hold is low and up/!down is high the counter counts up. When hold is low and up/!down is low the counter counts down.

   Only a decimal (digits 0-9) count should be displayed. The counter should count modulo 10.

4. The count frequency should be about 1 Hz.

5. The hold and up/!down inputs are to be synchronized at approximately a 10 Hz rate.

6. Clock signals are to be buffered through BUFG components.

7. All clocks should be nominal square waves.

Block Diagram

Refer to the Design Notes section for explanation of the diagram.

Design Notes

1. Each unique component shown in the block diagram should be designed as an individual VHDL entity using dataflow or behavioral VHDL. (Except for the components already provided, such as IBUF and BUFG.) Your top-level VHDL entity should, using structural VHDL, instantiate all needed components and connect them using signals.

2. Noting the following will save you from a major headache: the library and use statements must appear before each entity declaration, not just once at the top of the VHDL file.

3. Here is the schematic drawing for a synchronizer:
   

4. ``Frequency divider'' is a fancy term for ``counter.''

Test Driver

A test driver program will be available on the course home page. Executable and source code will both be available.

Assignment Turn-In

E-mail a copy of your commented VHDL source code and your .bit file to kelliher[at]goucher.edu.

Tom Kelliher