HFP: The time between the end of the horizontal active time and the start of the horizontal sync pulse is called the Horizontal Front Porch.
HBP: The period of time between the end of the Horizontal Sync pulse and the start of the next horizontal active time is the Horizontal Back Porch.
HSPW: The amount of time that the horizontal sync pulse is active is called the Horizontal Sync Width.
HSYNC is a signal given to the monitor telling it to stop drawing the current horizontal line, and start drawing the next line.
原文 (From: http://forums.entechtaiwan.com/index.php?topic=1620.0) :
HORIZONTAL AND VERTICAL SYNCS
When the beam reaches the right hand side of the screen, the monitor must be instructed that it is time to return the beam to the left side. Similarly, when the last scanline on the bottom of the screen has been displayed, the monitor must be instructed to return the beam back to the top of the screen for the next vertical cycle. The Horizontal Sync Signal and the Vertical Sync Signal, respectively, perform these functions.
Horizontal Sync Impulse
During the horizontal blank time, the monitor receives the horizontal sync pulse. The time between the end of the horizontal active time and the start of the horizontal sync pulse is called the Horizontal Front Porch. The amount of time that the horizontal sync pulse is active is called the Horizontal Sync Width. After receiving the horizontal sync pulse, the monitor returns the beam to the left side of the screen. The period of time between the end of the Horizontal Sync pulse and the start of the next horizontal active time is the Horizontal Back Porch. Adjusting the position of the horizontal sync pulse in relation to the horizontal blank time adjusts the location of the image on the screen to the right or left.
Vertical Sync Impulse
Similarly, during the vertical blank time, the monitor receives the vertical sync pulse. The time between the end of the vertical active time and the start of the vertical sync pulse is called the Vertical Front Porch. The amount of time that the vertical sync pulse is active is called the Vertical Sync Width. After receiving the vertical sync pulse, the monitor returns the beam to the tope of the screen. The period of time between the end of the Vertical Sync pulse and the start of the next vertical active time is the Vertical Back Porch. Adjusting the position of the vertical sync pulse in relation to the vertical blank time adjust the location of the image on the screen up or down.
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