<42/54> VDP1 User's Manual / 7. Commands

★ HARDWARE Manual ★ VDP1 User's Manual ★ Chapter 7 Commands

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VDP1 User's Manual / Chapter 7 Commands

■ 7.1 System clipping coordinate setting command

Clipping is to cut (clip) the area other than the set display area so that it will not be drawn. Clipping includes system clipping, which sets the drawing area of the system, and user clipping, which can be set freely by software.
When the command selection bit (bits 3 to 0) is 1001B, it is the system clipping coordinate setting command, and when it is 1000B, it is the user clipping coordinate setting command.
The table contents of the system clipping coordinate setting command are as follows:

bit 15 14 13 12 11 Ten 9 8 7 6 5 4 3 2 1 0 CMDCTRL +00 0 JP 0 0 0 0 0 0 0 0 1 0 0 1 CMDLINK +02 LINK designation / 8H 0 0 +04 +06 +08 + 0A + 0C + 0E +10 +12 CMDXC +14 0 0 0 0 0 0 Lower right X coordinate (XC) CMDYC +16 0 0 0 0 0 0 0 Lower right Y coordinate (YC) +18 + 1A + 1C 【note】 Is ignored (don't care)

The system clipping coordinate setting command is defined as follows.

Setting the end bit (bit 15) to 0B and the command selection bit to 1001B results in a system clipping coordinate setting command. Specify the jump format. When the jump format is assign or call, divide the address of the command table to be processed next by 8H and set it to CMDLINK. Define the lower right coordinates of the clipping area in CMDXC and CMDYC. The upper left coordinates are fixed at (0,0). The drawing area is on and inside the rectangular line represented by the upper left coordinates (0,0) and the lower right coordinates (XC, YC).

● System clipping

The system clipping coordinates are always enabled when drawing, and the outside of the set area is clipped. That is, the inside is drawn.

Clipping is done with a rectangle. Since the upper left coordinate is fixed at (0,0), the value of the lower right coordinate (XC, YC) is defined in the command table.

Since the clipping coordinates are not checked, set XC ≥ 0 and YC ≥ 0 in advance. Operation is not guaranteed if XC <0 or YC <0 is set.

Points on the clipping line are treated as inside the clipping area and drawn.

The clipping coordinate set command rewrites the internal clipping coordinate register. Subsequent parts that have been rewritten will be drawn with reference to that value.

This command can be defined as many times as you like in one frame, so you can have different clipping coordinates for each part group.

The system clipping coordinates have indefinite values after power-on or reset, so they must be set before drawing starts.

Figure 7.1 System clipping

(a) System clipping settings

The inside of the area is displayed

(b) Wrong system clipping settings

Operation is not guaranteed if XC <0 or YC <0 is set.

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★ HARDWARE Manual ★ VDP1 User's Manual ★ Chapter 7 Commands