Re: 42S display background matrix - Can it be "deleted"?


Took a long hard look at my 42S display today--ran the contrast up and down, tilted the screen away and toward me, etc. Results: 1) With fresh batteries, you can move from one contrast extreme to the other in 2 seconds by holding down EXIT and the + or - key. In a well-lit workspace, my personal preference was about 3/4 sec. darker than the minimum--i.e. about a third of the way up.
2) The angle at which you view the display can have a dramatic effect on what you see.
a) At 90,º directly above the display, I could barely see the entries at the minimum contrast setting. They were easily visible, however, when viewing from 30º-45º even at minimum contrast, and the dark part of the background had virtually disappeared.
b) At maximum contrast, viewing from 90º reveals that the layer of the display with the data on it actually casts a shadow on the dark background, which is made up of pixels. Viewed from <75º or so, the numbers appear lighter than the background--like a negative image, floating above the pixels. Maybe it's this separation or the shadows it causes that bother Dave Shaffer more than the background. You tend to get a double image until you learn to ignore it.
3) As for color, my entries read as deep greenish blue--like "Prussian Blue." I checked my 41CX and the numbers are the same color, though the background is lighter. There is a trade-off between the 41CX's superior contrast, and the more even and precise look of the 42S's typography, whose taller and narrower entries are easier to read: they allow more lateral display (12 vs 10 digits), cleaner separation between entries, and more room for punctuation.


I don't know about the 42S but other HP calculators with adjustable contrast have a finite number of levels. You might be able to hold "exit" down and then tap "+" and "-", counting the number of times to achieve different visual levels. Then you can relate them to something more precise than time.


The LCD contrast depends on a 5 bit value with can be modified by ON +/- in the range of #F - #1F.

The contrast register is located at

#40301 [CONT3 CONT2 CONT1 CONT0]


Becareful with Bit 3 of #40303 (DON = Display ON) this should be 1, SDAT and BIN must be 0! So only load #A or #8 into #40303. You can use the build in memory scanner to modify these values. A short description of the memory scanner could be found here


Please confirm: Do you mean that the range goes from 0F to 1F, so there are 16 valid values? The coding and bit layout doesn't seem very intuitive...


The possible range over the keyboard with ON +/- is from 0F-1F, the hardware supports the full range from 00-1F.

About the layout, the 5th bit for the MSB (CONT4) has to be placed somewhere, so Bit 1 in register #40303 was used.

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