● System register

• It is a memory for systematic setting of sprite IC, and is built in VDP1 separately from VRAM and frame buffer.

• There are read-only (read-only) registers and write-only (write-only) registers.

• Write-only registers are used to control the display of the framebuffer. Select TV mode, specify display switching and drawing triggers, and define the fill data and area of the erase light. You can also force the drawing to end.

• Read-only registers are used as help information during program development. You can know the address of the command table that was last rendered and the address of the command table that is currently being processed.

• Be sure to perform read / write access from the CPU in word units.

• Do not use DMA burst forwarding to access system registers.

• Except for the plot trigger register (PTMR), the value of the write-only system register is undefined after the power is turned on or reset, so be sure to set the value on the CPU. Indefinite data is displayed from the framebuffer until the appropriate value is set.

• Set 0 for unused bits in the write-only system register.