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Add calculation for caps >= 100pf to buck rogers LS626 frequency calculation.

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Formula was derived from figure 6 of LS624/628/629 & 625/626/627 datasheet.
"BUCK ROGERS" is now centered and big ship appears centered over br's ship.
Please Co-Credit Guru
This commit is contained in:
Couriersud 2009-01-27 23:39:44 +00:00
parent 4dbe268df4
commit b62bc23922
1 changed files with 22 additions and 11 deletions
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13
src/mame/video/turbo.c
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@ -249,6 +249,8 @@ INLINE UINT32 sprite_xscale(UINT8 dacinput, double vr1, double vr2, double cext)
vco_cv = 5.0;
if (vco_cv < 0.0)
vco_cv = 0.0;
if (cext < 1e-11)
{
if (vco_cv < 1.33)
vco_freq = (0.68129 + pow(vco_cv + 0.6, 1.285)) * 1e6;
else if (vco_cv < 4.3)
@ -260,6 +262,14 @@ INLINE UINT32 sprite_xscale(UINT8 dacinput, double vr1, double vr2, double cext)
/* up by a factor of 10 for every factor of 10 the capacitance is reduced */
/* approximately */
vco_freq *= 50e-12 / cext;
}
else
{
/* based on figure 6 of datasheet */
vco_freq = -0.9892942 * log10(cext) - 0.0309697 * vco_cv * vco_cv
+ 0.344079975 * vco_cv - 4.086395841;
vco_freq = pow(10.0, vco_freq);
}
/* finally, convert to a fraction (8.24) of 5MHz, which is the pixel clock */
return (UINT32)((vco_freq / (5e6 * TURBO_X_SCALE)) * 16777216.0);
@ -905,7 +915,8 @@ static void buckrog_prepare_sprites(running_machine *machine, turbo_state *state
info->plb[level] = 0;
info->offset[level] = offset << 1;
info->frac[level] = 0;
info->step[level] = sprite_xscale(xscale, 1.2e3, 500/*820*/, 220e-12);
/* 820 verified in schematics */
info->step[level] = sprite_xscale(xscale, 1.2e3, 820, 220e-12);
}
}
}