From: janl@ifi.uio.no (Jan Nicolai Langfeldt) Subject: Re: 110 MHz Tseng 4k card from Tseng Labs (selfhelp in desiding on card/monitor combo) Date: 26 Jul 1992 21:22:01 GMT
In article <1992Jul23.221019.20215@klaava.Helsinki.FI>, osmoviit@klaava.Helsinki.FI (Kari Osmoviita) writes:
> Somebody asked about faster than 80 MHz 4k card. I just ordered 110 Mhz
> version of Tseng Labs supervga card. It can show 1280x1024x16 colors at
> 60 Hz noninterlaced. For X386 at 1152x900 it could be quite nice with
> suitable monitor. I just wonder if Nanao/Eizo F550i (65 kHz line
> frequency limit) is good enough.
***TUTOR MODE: ON
Simple calculation (learnt from video tutorial):
How many horizontal pixels you want? = hpix = 1152
Dot clock? = dc = 110,000,000 (MHz = 10^6Hz)
line_frequency = dc/(hpix/0.8) =
110000000Hz/(1152/0.8) = 76388Hz =~ 77kHz
Which is clearly more than 65kHz. (also called horizontal frequency I
think)
Refresh_rate = line_frequency/(no_of_lines*1.05)) =
77kHz/(900*1.05) =~ 81Hz
So 77kHz horizontaly with 900 lines will give ~81Hz (vertical) refresh
rate.
110MHz is clearly for superior monitors.
Now you know all you need to know about what frequencies you can use
for what monitors. Lucky you! :-)
***TUTOR MODE: OFF
***SPECULATION MODE: ON
Going the other way: dc=110MHz and 65kHz line frequency given: You
need at least 1360 (1353 rounded up to be devidable with 8) horizontal
pixels to get down to 65kHz. 1Mb memory allows you 771 lines of 1360
pixels.
100MHz (and 1152x900) gives 69kHz and 73Hz respectivly. Which is
respective, but still demanding.
***SPECULATION MODE: OFF
But what is magic with 1152x900 (sun uses it?)? On most screens that
dosn't give square pixels. My monitor has 3/2 form factor, and is
limited to 57kHz horizontaly. I want square pixels, so after
calculating a bit 1120x746 seems to be ideal for my card/monitor
combination. Figuring out what my dot clock is and my vertical refresh
is left as an exercise for the reader :-) (easy pie!)
Nicolai
-- Nicolai Langfeldt, "Bugs made while you wait" Internet: janl@ifi.uio.no