Apple //e's RGB Card To Apple IIgs' RGB Monitor

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

Folks,



     I have seen Apple //e's RGB card is connected to Apple IIgs' analog RGB 
monitor using resistor network as the alternative option because digital RGB 
monitor is hard to find.

     Digital CGA monitor is recommended for best fit, but unfortunately, it 
gives wrong Apple II colors to be true 16 CGA colors.  It is what you don't 
want 16 CGA colors.

     Resistor network is ideal for Apple IIgs' analog RGB monitor, but it 
gives true 16 CGA colors!!  Are you satisfied?  No way.

     Look at RGBI to 12 bit RGB table below.



         RGBI  RED   GREEN BLUE  Hex

Color 0  0000  0000  0000  0000  000

Color 1  1000  0000  0000  1010  00A

Color 2  0100  0000  1010  0000  0A0

Color 3  1100  0000  1010  1010  0AA

Color 4  0010  1010  0000  0000  A00

Color 5  1010  1010  0000  1010  A0A

Color 6  0110  1010  0101  0000  A50

Color 7  1110  1010  1010  1010  AAA

Color 8  0001  0101  0101  0101  555

Color 9  1001  0101  0101  1111  55F

Color A  0101  0101  1111  0101  5F5

Color B  1101  0101  1111  1111  5FF

Color C  0011  1111  0101  0101  F55

Color D  1011  1111  0101  1111  F5F

Color E  0111  1111  1111  0101  FF5

Color F  1111  1111  1111  1111  FFF



     RGBI is Apple //e's video port of RGB card.  RED signal, GREEN signal, 
and BLUE signal are the 4-bit signal for analog RGB monitor for Apple IIgs.

     I got this information from several manufacturers who they manufactured 
CGA ISA controller cards.  Sometimes, people claim to say wrong color 
palette for VGA which wrong color palette made an attempt to match 16 CGA 
colors.  It is not important, but wrong palette seems to be satisfied.

     I borrowed this information and I wrote it into my own table above.  I 
can guarantee to be correct, but I am not 100% to be correct.

     Get rid of resistor network.  You don't need it.  Here is Apple IIgs' 
table below.  I got it from my own analysis using oscilloscope and Apple 
IIgs' hardware manual.



         RGBI  RED   GREEN BLUE  Hex

Color 0  0000  0000  0000  0000  000

Color 1  1000  1101  0000  0011  D03

Color 2  0100  0000  0000  1001  009

Color 3  1100  1101  0010  1101  D2D

Color 4  0010  0000  0111  0010  072

Color 5  1010  0101  0101  0101  555

Color 6  0110  0010  0010  1111  22F

Color 7  1110  0110  1010  1111  6AF

Color 8  0001  1000  0101  0000  850

Color 9  1001  1111  0110  0000  F60

Color A  0101  1010  1010  1010  AAA

Color B  1101  1111  1001  1000  F98

Color C  0011  0001  1101  0000  1D0

Color D  1011  1111  1111  0000  FF0

Color E  0111  0100  1111  1001  4F9

Color F  1111  1111  1111  1111  FFF



     How do you do this to make Apple //e's RGB card work with analog RGB 
monitor using this table above?  Forget about resistor network.  You will 
need 5 chips.  Simple?  Yes, it does!!

     First of all, you need to program this table above.  RGBI is the four 
input pins.  RGB is the 12 output pins.  You can write it using EPROM chip. 
I suppose that 4 bit is to be address bus and 12 bit is to be data bus, but 
EPROM chip might not be the answer for you.  It may need two or three EPROM 
chips.

     You can program using two GAL16V8 chips.  Two GAL16V8 chips are enough. 
Are you satisfied to have 12 bit RGB pins to be 12 digital signals?

     The problem is the analog RGB monitor.  It can't accept 12 digital 
signals.  You need three chips.  It is 4 digital bits to 1 analog bit 
convertor.  One for Red chip, Green chip, and Blue chip.

     After you have assembled five chips together from digital RGBI to 
analog RGB, Apple //e's RGB card outputs picture to Apple IIgs' analog RGB 
monitor using correct Apple IIgs' 16 colors.  Are you satisfied?  Yes, of 
course.  It goes!!

     It is my thought to suggest, but I have never done with this project 
yet.  Please let me know if you can use my information to develop your own 
project.



     Please comment what you think.



Bryan Parkoff