Explanation of words

The terms used in this manual are explained below.

VDP1

VDP1 is an IC that controls drawing. VRAM and frame buffer (both DRAM) are connected to VDP1. Drawing commands are written from the CPU to VRAM via VDP1. VDP1 reads the drawing command from VRAM, writes (draws) the drawing data to the frame buffer, and then transfers the drawing data from the frame buffer to the display device for display.
The frame buffer is a so-called bitmap memory, and there is a one-to-one correspondence between the data written in the frame buffer and the contents of the display screen. The frame buffer is a mapping of the display screen. There is a system register inside VDP1, and the display of the screen is controlled by setting a value in this register.

display

The display uses a TV, which is a general display device. The domestic and American TV standards are NTSC. European TV is PAL.
High resolution is an increased resolution that doubles the horizontal resolution. 31KC is a method in which the horizontal frequency is doubled from the normal 15KC in order to increase the vertical resolution. High-definition television (HDTV) is a so-called high-definition television, which has twice the resolution both vertically and horizontally compared to ordinary TVs.
The TV display has fields and frames. The field is the time that the scan line scans one screen. It takes 1/60 seconds for the NTSC method and 1/50 seconds for the PAL method. The frame is the period during which one image is displayed. One frame is from the switching of the frame buffer to the next switching. When the frame buffer switching mode is 1 cycle mode, 1 frame is 1 field. If the frame buffer is switched every two fields due to single-dense interlacing, one frame becomes two fields. If you switch only once per second in manual mode, one frame will be 60 fields in NTSC and 50 fields will be in PAL.
The framebuffer is automatically erased before drawing each frame. Erasing is performed by writing (filling) the code specified in the register to the frame buffer. This erase and write operation is called erase light.

access

Reading and writing VRAM, system registers, and framebuffer data from the CPU and VDP1 is called access. Arbitration is used when accessing VRAM, system registers, and frame buffers. Arbitration is to prioritize when two or more devices access at the same time. Writing usually takes precedence over reading for drawing.
With the DMA controller, access to VRAM can be done continuously and at high speed with burst transfer. However, do not burst access to the register.

data

A bit is the smallest unit of data that represents 0 or 1. 8 bits are collectively called a Byte, and 16 bits (or 2 bytes) are called a word. When the upper and lower bytes of a byte are divided into 4 bits, each is called a nibble.

command

Commands include drawing commands, clipping coordinate setting commands, and relative coordinate setting commands. Clipping cuts the shape outside the set area. Relative coordinates change the drawing position using the specified coordinates of the drawing command as relative coordinates.
Commands are defined in VRAM as a command table. In addition to the command table, the table includes a character pattern table, a Gouraud shading table, and a color lookup table.
The table is defined and stored in VRAM from the address of 8HByte boundary or 20HByte boundary. Boundary means that when the address is divided by the values 8H and 20H, it is completely divisible. The register has a 2HByte boundary.
VDP1 fetches the command table one after another and draws according to the command. Fetching is reading from VRAM to process a command.

parts

What is drawn by the drawing command is called a part. Parts are divided into textured parts and non-textured parts. The texture parts are sprites. Non-textured parts include polygons, polylines, and lines.
Sprites are so-called characters. The character defines the character's color code in VRAM as a character pattern table. Polygons are filled rectangles, polylines are unfilled rectangles, and lines are straight lines connecting two points.
VDP1 processes drawing commands in VRAM to draw the part into the framebuffer. Drawing is done in pixel units. The data on the frame buffer expresses color in 16 or 8bit / pixel.

Color

There are two color expression methods: RGB code method and color bank method using palette code and color bank.
The RGB code method expresses colors by specifying the brightness of each of red (R), green (G), and blue (B) with 5 bits.
In the color bank method, select the VDP2 color palette in the color bank and select a color from the color palette in the palette code.
Sprites can also specify colors using the color look-up table method. Define 16 colors in the color lookup table and select a color from them. The color code can be specified as either RGB code or color bank code.

Color calculation

Color calculation is a special function of VDP1. Gouraud shading is a color operation. Change the brightness of the RGB code of the part with the four RGB codes defined in the Gouraud shading table.

Manual notation

The notation of this manual is as follows.

Binary and hexadecimal

Binary numbers are written with a B at the end. For example, it is expressed as 100B. However, when it is 1 bit, B may be omitted.
Hexadecimal numbers are written with an H at the end. For example, it is expressed as 00H and FFH.

unit

1KByte represents 1024Byte. 1Mbit is 1,048,576bit.

MSB, LSB

The composition of bytes and words is that the left represents the high-order bit (MSB, most significant bit) and the right represents the low-order bit (LSB, least significant bit).

Undefined bit

Bits not defined in the command table and system registers are represented by "-".
Write 0 to the undefined bit in the system register.
Don't care when all one word is unused on the command table. You can write either 0 or 1. If there are used bits in one word, fill the remaining unused bits with 0s.

Address, address

The address shown in this manual represents the relative address of VDP1. VDP1 is located at the absolute address 5C00000H of the system.
Add 5C00000H to find each absolute address.
For example, the absolute address of VRAM of 000000H is 5C00000H, and the absolute address of the system register of 180000H is 5D80000H.