Re: HGR Displays During HBL?

[heuser.marcus@freenet.de]

Bryan Parkoff wrote:
> You may notice magenta (deep red) color appears in the screen during
> HBL.  You can type below like this in Applesoft BASIC prompt.
>
> ]HGR
> ]HCOLOR=5: HPLOT 279,0 TO 279,191
> ]HCOLOR=4: HPLOT 0,0 TO 0,191
>
>     Do you notice that orange vertical line becomes brown in the far right?
> I know that it is cut-off, but did you see magenta vertical line in the far
> left?  If you fill 0x40 in memory address: 0xXXFF, it will fill magenta
> vertical line from line 0 through the middle line.
>     It has a bug on Apple II+, but Apple //e has fixed the bug.  Can you
> please explain why Apple II+ has reproduced bug for curiousity?  0xXXFF can
> have data, but they are not supposed to be displayed during HBL which it
> must always be undisplayed.  It is how magenta vertical line detects 6th bit
> of data bus which it is turned on to form magenta vertical line while
> vertical line in position 0 is always filled with 0x80 (delayed black).

You should google a bit in this group - I'm pretty sure that this has
already been explained.

Here is an old example to display 12(!) different *real* colors - the
catch: This only functions on certain horizontal coordinates and with
certain bit patterns:

 5  PRINT  CHR$ (21)
 10  TEXT : POKE 34,20: FOR C = 0 TO 15: HGR : HOME : READ C1,C2,X
 15  IF  PEEK (65055) - 96 THEN  POKE 49204,C
 20  PRINT "Color "C;: IF X < 0 THEN  PRINT " is unavailable";: GOTO 50
 30  FOR X = X + 6 TO 273 STEP 14: HCOLOR= C1: HPLOT X,0 TO X,150
 40  HCOLOR= C2: HPLOT X + 1,0 TO X + 1,150: NEXT
 50  PRINT : PRINT : INPUT "Press return...";X$
 60  NEXT
 1000  DATA 0,0,0
 1001  DATA 0,0,-1
 1002  DATA 7,0,0
 1003  DATA 3,0,0
 1004  DATA 0,0,-1
 1005  DATA 0,0,-1
 1006  DATA 7,4,0
 1007  DATA 3,4,0
 1008  DATA 7,0,7
 1009  DATA 7,4,7
 1010  DATA 0,0,-1
 1011  DATA 7,3,7
 1012  DATA 0,3,0
 1013  DATA 3,4,7
 1014  DATA 7,3,0
 1015  DATA 3,3,0

Line 15 is only for GSses to demonstrate that the resulting colors are
identical with the ones in the border (the POKE sets the border color).


>     Is it possible that the designer made mistake to design Apple II+'s
> motherboard with TTL chip?

This is a joke, right?

bye
Marcus