Re: Apple ][ to VGA monitor adapter board - looking for best color decoding method

[David Wilson <mcs6502@gmail.com>]

On Apr 5, 9:02 am, ferd...@gmx.de wrote:
> The Apple //e's PAL encodes uses a circuit with a quad D-FF, but I
> don't know how it is wired.
> So I'm looking for the schematic of the //e's PAL encoder or the PAL
> color card for the ][.

Jim Sather published the IIe PAL circuit in "Understanding the Apple
IIe" (page 8-18).

The basic logic is as follows:

SEROUT*  => LS164-1
ALTVID* => LS164-2
14M => LS164-8

LS164-6 => LS175-4 (D3)
LS164-10 => LS175-13 (D0)
LS164-11 => LS175-12 (D1)
LS164-12 => LS175-5 (D2)

R-Y = Q0 via 2.2k + Q2* via 2.2k
B-Y = Q0* via 2.2k + Q1 via 1k + Q2 via 2.2k + Q3* via 1k

There is slightly more circuitry involving the color gate before the
color difference signals reach the encoder chip. I will see if I can
find my photo of that page.