Digitala Projekt VT 2017
The goal of this project was to build a VGA signal generator based around a Motorola 68008 CPU. The system contains the CPU, a 10 MHz clock- module, reset circuitry, SRAM chip, EEPROM chip and 2 PAL (22V10) circuits. One of the PAL circuits is used for address decoding and the second chip functions as an interface to a virtual VGA-chip. The goal was to have the system generate a standard VGA resolution, 640x480 with a refresh rate of 60 Hz.
(prototype on a breadboard)
All VGA signals are generated in software that is run by the 68008 CPU, and requires that every cycle during a frame is accounted for. If the cycle count is not correct the signal might not become viable for a VGA display unit. During the project it was also apparent that the 68008 CPU is far from ideal to send data from RAM to the VGA circuit. The clockspeed was to low and the average cycle count per instruction was to high. As a compromise, only one color change was made per line, resulting in what is called raster bars.
(programmer used during the project)
The course gives the student a lot of practical experience with contructing with electronics, programming and utilizing different tools, such as logic analyzers, asemblers, compilers and more. It is a great mix of studing components datasheets and then appliyng this knowledge in a practical setting.
(rasterbars example)
The full report can be found here