Adafruit EGA (I think) from arduino

jwsmobile jws at
Wed Apr 15 23:06:22 CDT 2015

I think what they are doing here is driving an EGA monitor in CGA mode 
with an arduino.

That seems to be a handy thing to have in an old computer bag of tricks.

i'd also like to have a circuit to grab semi static video off of CGA or 
EGA ports into Arduino.  I'll post another bit with a sync generator 
shield for Arduino for that purpose.

You may need to be on Google plus to get the following.  I'll post the 
text below the Adafruit link which is mentioned in the post.

*CGA Output to IBM Enhanced Color Display from Teensy 3.1*

Benjamin Gould made this cool project with his CGA monitor using Teensy 
via paradigm lift

/A while back, while hunting for an IBM PC AT Model F keyboard, I came 
across a Craigslist ad that said something like “IBM Model 570 computer 
for sale with monitor and keyboard, $50″. I realized that it was 
probably a typo and that they meant Model 5170, which was the IBM PC AT. 
To make a short boring story shorter, the keyboard with the system was a 
1986 Model M instead of Model F, but by itself was worth more than $50 
anyhow so I lugged the whole thing home and sold the keyboard to cover 
the cost. I set the PC and monitor aside for a while until I became 
curious if you could drive the monitor with a microcontroller, and I 
came across this post on // <>//./

/The aforementioned post featured a project by a hacker who was able to 
get a signal from his Arduino Uno to show up on a CGA monitor. His 
demonstration only had horizontal lines, which is much easier than 
sending individual pixels. Still, his proof of concept project was very 
encouraging and gave me a great jumpstart on the timing calculations 
that I would need. Here’s some quick notes regarding the scanning:/
/• The pixel clock for CGA was 14.31818 MHz. Take the reciprocal of that 
i number (1/14318180) to find that it takes about 0.06984 microseconds 
/• CRT display has electron emitting beams that are rapidly moved across 
a phosphor screen to create an image. At the end of each line the beams 
are turned off as they move back to left side of the screen and down 1 
pixel. After the last visible horizontal scan line they are also turned 
off long enough for the beams to retrace vertically./
/• In between each horizontal and vertical scan, a synchronization 
signal is emitted as well. For CGA, there are dedicated HSYNC and VSYNC 
lines that carry these signals./

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