FPGA VGA Resistor DAC

           VGA is a very friendly protocol to use with FPGA's and CPLD's and because of this we can easily build video controllers with basic PLDs. The VGA protocol itsself is slow, running around the 20-30 MHz range depending on the resolution chosen, meaning that we can even breadboard or wire-wrap prototype designs!
           This tutorial will continue using the CPLD development board made previously and add some VGA hardware in order to make a 512 color VGA controller. The CPLD that we will use is an Altera EPM7128 which is widely available for purchase. It is also relatively old, but does the trick for this tutorial.



CPLD Dev Board + VGA Hardware - Action Video

CPLD Dev Board + VGA Hardware (Top)

CPLD Dev Board + VGA Hardware (Bottom)

Purpose & Overview of this project
           The purpose of this tutorial is to modify the CPLD development board so that it can output 512 colors to a VGA monitor. This will be done using a 9 resistor DAC (digital to analog converter) connected to 9 pins on the FPGA. A 25.175 MHz can oscillator will also be needed for the global clock input signal into the CPLD.
           The language of choice to use with the CPLD and Altera's tools will be VHDL. Please be sure you're familiar with VHDL before continuing or at least take a look at the Introduction To VHDL tutorial. Since we're using an Altera FPGA, that means we will need to also use the Quartus II development enviornment.