Re: Challenge!

 BBS: Inland Empire Archive
Date: 11-19-92 (02:35)             Number: 313
From: RAYMOND KEITH                Refer#: NONE
  To: RICH GELDREICH                Recvd: NO  
Subj: Re: Challenge!                 Conf: (2) Quik_Bas

> 'Here's a challenge for anybody who thinks they can figure it out:
> '    Explain HOW this program shows more than 16 colors in a 16
> '    color mode.

Your basicly updating the color palette while the display is in a horizontal
retrace period.

(1) The Input Status #1 register through port &H3DA gives you access to
the VR field (Vertical Retrace) and the DE field (Display Enable NOT).
These will let you know when to update the palette.

(2) &HC7 is the Pel address read mode register which
contains the eight bit address used to access one of the
256 color registers during a read opteration.

(3) &HC8 is the Pel Address write mode register which contains the eight bit
address used ot access one of the 256 color registers
during a write operation.

(4) &HC9 is the Pel data register which is a 18 bit wide register used to
interface the host and the 256 color registers. Each color register can hold
the primary colors, Red, Green, Blue. Each takes 6 bits. Since the host data
bus is only 8 bits you can only change one color at a time. The registers
above through &HC7 and &HC8 note which color register is
being read or written to with the data in this register.

Well you get the idea, wait for a horizontal retrace period, then change
a color, etc. Rich I think that is what your doing. If not, my answer is
surely techy looking enough to fool some people. <wide smile>

Raymond

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