A frame is a screen's TRUE width/height, measured in the PIXEL unit (PIXEL/TIME would be more precise, but not necessary) including the sync pulses, the blanking periods, the displayed pixels and some safety room. To get the FRAME SIZE from the DISPLAY SIZE, we must factor (multiply) the desired DISPLAY SIZE:
H-framesize ~= Display Width * 1.25 V-framesize ~= Display Height * 1.10See:
1. What is a screen made of, how is it drawn?
2. Should I ever adjust the Frame Size? Why?
A FREQUENCY means a number of times an event occurs during a determined period of time, for a second this unit is called Hertz or Hz for short. A single Hz is 1 event in 1 second, so a refresh rate of 60 Hz means 60 refreshes per second. KHz is the same but multiplied by a thousand, so 1 KHz is 1000 events in 1 second, and 1000 KHz is 1 Mhz.
Since your graphics card works in the PIXEL unit, any and all frequency measurements you see represent a number of pixels! A bandwidth of 36Mhz for example, on a 640x480 screen (frame size is 800x520), means that every second 36,000,000 pixels are written or sent out. This total number of pixels is thus the number of times the square that is the screen (width * height) is drawn per second:
36Mhz = (800 x 520) x ?? Refresh = 36,000,000/(800x520) ~= 86Hz
Again, anything you see in "Hz" is just a number of pixels per second. And thank the Gods you don't have to worry about the width of each pixel ;-)
The horizontal line frequency is the speed at wich each line must be read/sent by the graphics card in order to reproduce a full screen's worth every 1/FrameRate second. Say you have a 800x600 screen that is refreshed every 1/60th second (60Hz), that means the card has to read/send 600 lines (more when you count the entire frame) of data every 1/60th second, and thus the frequency at which each line is read is:
HLineFREQ (KHz) = VFramesize * SCANRATEThis value is calculated for you if you use P96M, you use the frame and the pixel clock to adjust it instead. You will use it in TNG however, since you do not have access to the frame size. This value can also be used in bandwidth calculations, basically anywhere you need the one of the terms of the equation when you have the other two.
The SCAN RATE is the number of frames drawn per second, for a particular screen mode. The higher this value (which is in Hz), the steadier the display. Just how many frames you can get your card to draw depends on the maximum bandwidth your card can deliver, and on the size of the display mode. When talking SCANRATE, remember the following:
SCAN RATE == REFRESH RATE == VLineFREQ == #Frames/s SCANRATE (Hz) = HLineFREQ / VFramesize VFrameSize / 2 = RefreshRate * 2 HFrameSize / 2 = RefreshRate * 2 & HLineFREQ * 2 MEMORY BANDWIDTH (MHz) == PIXEL CLOCK * BytesPerPixel Max#Frames = MaxMBW / ((dWIDTH * 1.25) * (dHEIGHT * 1.10) * BBP))See:
2. Should I ever adjust the Frame Size? Why?
6. Video/Memory Bandwidth and Pixel Clock explained!
7. Useful formulas for TNG. and 8. Useful formulas for Picasso96mode.
The SYNC PULSE is a square PULSE (a peak if you wish) in the video signal, telling the monitor that yet another line or screen has been completely sent by the graphics card. The monitor times the interval between these pulses and determines the frequency at which the data is sent. It's size is measure in pixels, which are a TIME unit, since a pixel is 1/PixelClock amount of seconds.
This PULSE is preceeded and followed by a period of "BLANK" signal to help identify the pulse from the rest of the data. This blank signal is what is called the BLANKING PERIOD, and it is very much needed. Too little blank time and the monitor will not enter in "sync pulse search mode," and will be unable to gather timing information.
A synchronization sequence looks similar to this on an oscilloscope:
1v PULSE ******* * * BLANK * * BLANK 0v ********** ********** ---> timeSee:
1. What is a screen made of, how is it drawn?
3. What effect does the Sync Size have?
4. What is the Sync Polarity?
-- /\ / Sylvain Bourcier - Booze@Videotron.CA - BeID7789 \ mEMBER:-World-Wildlife-Fund-+-DSF-+-Planetary-Society-+-Team-Amiga- \C:\DOS\SYSTEM\OS2\UTILITIES\DOCS\HELP\WHERE\THE\F$#%\AM\I???
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