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(MESS) a7800.c - Added more details and clarification regarding the potentiometer. [Robert Tuccitto]

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Scott Stone 2014-02-20 20:15:26 +00:00
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1 changed files with 45 additions and 7 deletions
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src/mess/drivers/a7800.c
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@ -74,8 +74,12 @@
2014/01/02 Robert Tuccitto Corrected joystick buttons assignment & minor 2014/01/02 Robert Tuccitto Corrected joystick buttons assignment & minor
palette notes cleanup. palette notes cleanup.
2014/01/09 Robert Tuccitto Positional description for difficulty
switches added. 2014/01/09 Robert Tuccitto Positional description for difficulty
switches added.
2014/02/15 Robert Tuccitto Added more details and clarification
regarding the potentiometer.
***************************************************************************/ ***************************************************************************/
#include "emu.h" #include "emu.h"
@ -171,12 +175,46 @@ depending on how poor or well it handles the signal conversion and its
calibration) on a modern flat panel display, as opposed to 'gold' (~-33 calibration) on a modern flat panel display, as opposed to 'gold' (~-33
degrees) on a CRT. degrees) on a CRT.
The system's pot adjustment manually manipulates the ratio of blue to The potentiometer (pot adjustment) for the 7800 modifies the delay line
green/blue to red, while the system 'warming-up' causes the palette phase regarding colors it will exhibit and is extremely sensitive. The slightest
shift to go higher in degrees. turn can have a significant impact.
At power on, the system's phase shift appears as low as ~23 degrees and A system whose potentiometer is not properly calibrated via
after a considerable consistent runtime, can be as high as ~28 degrees. 'CPS 7800 Diagnostic Test Cartridge' or/and just slightly off from the
desired factory settings may exhibit consequences such as too much blue in
place of green (Pot adjusted slightly too far left) or washed out reddish
tones in place of where most other systems display a darker reddish tones
(Pot adjusted slightly too far right).
This is a result of the phase shifting of lesser degrees (Pot adjusted more
to the left) or phase shifting of greater degrees (Pot adjusted more to the
right).
Turning the pot adjustment to the right, it can be observed that the values
of the higher end of the scale will match the lower end of the scale.
For example, after some turning to the right, the values of Dx, Ex, Fx,
can be set to match 1x, 2x, 3x.
After further turning to the right, now the palette can be brought to make
Ax, Bx, Cx, Dx, Ex, Fx will match 1x, 2x, 3x, 4x, 5x, 6x.
Ultimately though, too much turning to the right results in all colors being
wiped from the scale, excluding the hue begin point 1x (Which remains
unchanged while tweaking the potentiometer either left or right).
Continuously turning the pot adjustment to the left, red and blue become the
most dominant two colors encompassing the palette with only a slight
influence of green at the highest end of the palette (Fx), once turned all
the way leftward.
The degree range for adjustment of the phase shifting on the 7800 appears
to be as low as approximately 15 degrees when tuned all the way left, and
seems to be able to achieve as high as approximately 45 degrees when turned
right before losing all color (Excluding 1x) from the palette scale.
For even a properly calibrated system at power on, the system's phase
shift appears as low as ~23 degrees and after a considerable consistent
runtime ('warm-up'), can be as high as ~28 degrees.
In general, the low end of ~23 degrees lasts for maybe several seconds, In general, the low end of ~23 degrees lasts for maybe several seconds,
whereas higher values such as ~25-27 degrees is the most dominant during whereas higher values such as ~25-27 degrees is the most dominant during