Re: Apple //e's inverted screen?

["Bryan Parkoff" <nospam@nospam.com>]

"David Wilson" <mcs6502@gmail.com> wrote in message 
1159751125.836906.154290@b28g2000cwb.googlegroups.com">news:1159751125.836906.154290@b28g2000cwb.googlegroups.com...
> Bryan Parkoff wrote:
>>     Okay, lets say if ALTVID' has low signal.  Will the screen be 
>> inverted
>> including inverted 16 colors?

David,

> No. As I said - if ALTVID' is low, the video will be high (white if
> ALTVID' is low for at least 2/7 of a microsecond).
>
>>  Will it show white border in the top, bottom,
>> left, and right margin?
>
> The margins are normally black due to the signal WINDW' (aux-7) from
> the IOU chip driving OE' on the chargen. As ALTVID' is connected after
> the LS166 parallel->serial chip this means that ALTVID' can even
> override the black margins. So yes, you can use ALTVID' to make the
> margin white.

    I understand.  It makes sense when NAND gives 4 possible data 0, 1, 1, 
and 1.  If ALTVID is high, it allows LS166 to flow serial bit stream through 
an inverter '0' to '1' and '1' to '0' so '0' and '1' is used for output of 
NAND.  If ALTVID is low, the output of NAND is '1' and '1'.  I agree that 
the background is solid white if ALTVID is low.  My question is -- would the 
border be white?  You claim to be black border with white background, but I 
claim white border and white background.
    I agree that WNDW is high to disable VIDEO ROM chip to stop flowing 8 
bit parallel data to LS166 chip however load/shift register is still loaded 
with "11111111" or 0xFF during high WNDW.  Then "11111111" is shifted out 
through inverter inside NAND to be "00000000" so border is black during 
blanking.  If you replace NAND chip to inverter chip while it ignores 
low/high ALTVID, the result is the same as before.  If you remove NAND chip 
and allow LS166 chip to be shifted out to the video signal directly without 
through NAND / inverter, you will see white border and inverted 16 colors.
    Does it make sense?  Why is ALTVID needed?  I guess that if RGB card is 
installed in aux card to block the users from viewing NTSC monitor.  I use 
RGB card, but it allows me to view RGB monitor and NTSC monitor at the same 
time.

Bryan Parkoff