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Re: Apple //e's inverted screen?
- Subject: Re: Apple //e's inverted screen?
- From: "David Wilson" <mcs6502@gmail.com>
- Date: 30 Sep 2006 22:45:05 -0700
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Bryan Parkoff wrote:
> Is there a possibility that Apple //e's screen will have white border
> including left, right, top, and bottom margin on NTSC monitor? Bit stream
> is always inverted before it is shifted out to the NTSC monitor. If you
> bring ALTVID signal to high, it would block the inversion while it continues
> to shift out without being inverted.
> I assume that 16 colors are inverted.
ALTVID' (aux slot pin 27) has a pull up resistor so making it high is
already the default.
If you assert it (logic 0) then the screen will be white. It does not
block the inversion (C5 is a NAND gate operating as an OR gate with
inverted inputs and not an XOR gate).
If you take ENVID' (aux-29) high (it has a pull down resistor) the
outputs from the chargen will be disabled and pulled high by RP3
resulting in black.