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hardware:color [2018/03/05 20:31]
ex_writer [Horizontal Color Boundary]
hardware:color [2018/03/05 20:33] (current)
ex_writer [Horizontal Color Boundary]
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 ==== Horizontal Color Boundary ==== ==== Horizontal Color Boundary ====
  
-A horizontal color boundary register (HORCB) defines the horizontal position of a vertical line that divides the screen into the left and right color palettes. The boundary line can be positioned between any two adjacent screen bytes. The line is immediately to the left of the byte whose number is sent to bits 0–5 of port 9. For example, if the horizontal color boundary is set to 0, the line will be just to the left of byte 0; if it is set to 20, the line will be between bytes 19 and 20 in the center of the screen.+A horizontal color boundary register (HORCB) defines the horizontal position of a vertical line that divides the screen into the left and right color palettes. The boundary line can be positioned between any two adjacent screen bytes. The line is immediately to the left of the byte whose number is sent to bits 0–5 of output ​port $9. For example, if the horizontal color boundary is set to 0, the line will be just to the left of byte 0; if it is set to 20, the line will be between bytes 19 and 20 in the center of the screen.
  
 The left/right bit is an additional register identifying signal supplied by the video processor in response to the data stored in the horizontal color boundary register. If a pixel is to the left of the boundary, its left/right bit is set to 1. The left/right bit is set to 0 for pixels to the right of the boundary. Color registers 0–3 are used for pixels to the right of the boundary and registers 4–7 are used for pixels to the left of the boundary. If a byte read from display RAM has the values 00 11 10 00, and was to the right of the boundary line, for example, the four pixels will be defined by color registers 0, 3, 2, and 0, respectively. However, if the byte is located to the left of the horizontal color boundary line, the four pixels will be defined by color registers 4, 7, 6, and 4 respectively. The left/right bit is an additional register identifying signal supplied by the video processor in response to the data stored in the horizontal color boundary register. If a pixel is to the left of the boundary, its left/right bit is set to 1. The left/right bit is set to 0 for pixels to the right of the boundary. Color registers 0–3 are used for pixels to the right of the boundary and registers 4–7 are used for pixels to the left of the boundary. If a byte read from display RAM has the values 00 11 10 00, and was to the right of the boundary line, for example, the four pixels will be defined by color registers 0, 3, 2, and 0, respectively. However, if the byte is located to the left of the horizontal color boundary line, the four pixels will be defined by color registers 4, 7, 6, and 4 respectively.