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If you could replace a single colour on the 9918’s colour palette with any RGB value, what colour would you add, and which would you remove?

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I would have really like it if TI had gone with a default of white on dark blue in Extended BASIC instead of black on cyan.  Who knows why, maybe because it looked sharper on old CRT monitors or TV's of the era?  I dunno.

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My experience is (also with current webpages) that bright text color on very dark background cause strong afterimages (for seconds) in my eye. The worst is, of course, white text on black background. Usually, I change the color scheme of my Linux terminals to dark letters on bright backgrounds.

 

The white on medium blue of Editor/Assembler seems to be OK, though.

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On 12/18/2019 at 9:40 PM, Airshack said:

Why does the TI-99/4 have this color pallet? Why multiple shades of yellow, red, blue, green? I’ve always wanted to know. Is it really just eight colors somehow hacked into 16 via digital sorcery? Why no brown or dark grey? Why a less spectacular pallet than one witnesses playing Atari VCS games?

This one we DO have an answer to, via Karl Guttag. This was on the Yahoo TI99-Dev group on Jun 3, 2011. It gets a bit technical, and is more about the how than the why, but there are some hints of meddling that may explain the why. ;)

Quote

 

The composite video was done rather crudely.

 

The was a phase delay chain (Fig 10 of the patent) that generated the
various phases for the color signals.   They made the inverters 338 to 354 a
little bigger or smaller to get some analog tweaking to tune the delay at
finer than the clock phase level (and they tweaked the strengths and thus
tuned the color phase a few times in the early years).    This gave all the
phases (relative to color burst) that were available.  BTW, it was TI's home
computer engineers that told us how they wanted the circuit tweaked (it may
have been even one of them that came up with basic idea although Joe Sexton
did the actual design).

 

The amplitude of the signals were controlled by the "analog/voltage
multiplexer" shown in Fig 11.  The phases were then used to tap a long
resistor (made of polysilicon -- essentially doped glass) .  This resistor
had many taps on it to select a voltage from the resistive divider.
Early-on they changed the tap points to tweak the intensity.   So very
simply,  the "phase" was given by the circuit in figure 10 and the amplitude
for was given by the tap point on the resistor.

 

The reason for the "offset" was the need to run the output Transistor 376 in
 in a linear range with voltage "multiplexer" of Fig 11.  The transistor
would only work correctly when the source, gate, and drain were in the right
voltage range.    As I remember it (some 33 years later), it was assumed
that the composite video would be capacitively coupled to the video input so
that the DC voltage offset didn't matter (I think the manuals many have even
said this someplace -- I will have to look).  There really was not a lot of
analog design done on the 9918, so this was the simplest solution, just
leave the output transistor biased up into the right range with the follower
circuit an and external pull down.

 

 

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15 hours ago, Tursi said:

This one we DO have an answer to, via Karl Guttag. This was on the Yahoo TI99-Dev group on Jun 3, 2011. It gets a bit technical, and is more about the how than the why, but there are some hints of meddling that may explain the why. ;)

 

Third grade English translation requested.

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5 hours ago, Airshack said:

Third grade English translation requested.

The colors are hard wired inside the chip and there was meddling from all the other groups about the exact colors. ;)

 

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