Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!samsung!bragi!dj
From: dj@bragi.ctron.com (DJ Delorie)
Newsgroups: comp.os.msdos.programmer
Subject: Re: MSDOS monochrome displays?
Message-ID: <1406@bragi.ctron.com>
Date: 8 Apr 91 21:25:55 GMT
References: <3586@naucse.cse.nau.edu> <1399@bragi.ctron.com> <1991Apr08.184731.8800@proto.com>
Organization: None whatsoever
Lines: 32

In article <1991Apr08.184731.8800@proto.com> joe@proto.com (Joe Huffman) writes:
>dj@bragi.ctron.com (DJ Delorie) writes in an otherwise flawless posting:
>
>>An EGA with a vanilla mono monitor (ie: from an MDA) is limited to
>>four greys again, because the monitor only watches two of the TTL
>>signals.
>
>EGA mode 0x0F (for use with the "vanilla ... MDA") has four "colors".  
>Black, white (green on the IBM 5151), high intensity white, and blink.  
>Blinking pixels on the screen would appear to have little use in simulating 
>another shade of grey.

You can shut off the blink with a BIOS call (or if not, through
hardware), giving you:

black
"intense" (dim)
normal
normal & "intense"

The monochrome monitor has two digital inputs, for a total of *four*
intensity levels.  The EGA card is capable of driving the lines in all
four states, giving four available intensity levels.

The *default* behavior, however, is to simulate blinking for the
benefit of backward compatibility.

I know it works this way because I wrote a graphics terminal emulator
that used EGA, vanilla Mono monitor, and mode 0x0f, and it produced
four levels of intensity - and no blinking.

DJ