Electronics » Z80 Laptop Project... GFX board
V4 Z80 graphics board |
The V4 graphics engine is, like the mainboard, based on a small FPGA (Xilinx XC2S30 Spartan 2).
This has allowed quite step up in power from the V3 graphics system and also removed the need for
the microcontrollers which were originally handling the sprites and timing elements. Briefly,
here's what's new:
Palette increased to 12bit (4096 colours)
256 colours on screen at once - 8 bitplanes.
16x16 pixel tile map mode with dual playfield
Number of sprites per line increased to 56
Simple blitter - much faster moving data in VRAM than CPU.
All the usual features like hardware scrolling, double buffer remain. The system runs at
16MHz - plenty fast enough for what I wanted to achieve without requiring any FPGA timing constraints.
Testing the bitmap mode.. |
There's not a lot of components on the gfx board. There could've been even less but I needed all
the available FPGA pins and had to latch / buffer the video output lines (achieved by the 3 x 74HC574
ICs you can see at the top, feeding the resistor colour DAC). There's two 128KB 12ns static RAMs,
one for the main video memory and one to hold the sprite data. Not visible on the top side of the PCB
are: A serial EEPROM (24C512) and PIC 12F629 which supply the FPGA configuration pattern on power up,
decoupling capacitors for the FPGA and a connector for the mainboard.
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