Using the DEC VR241 with IBM CGA [I can't take much credit for this article. What I have written here has been pulled together from notes several other people have written. Thank you to all who contributed. -gary-] It is possible to use a DEC VR241 color monitor with an IBM CGA card (or an EGA card operating in CGA mode). However, a special cable that changes the voltage levels is necessary. The EGA card uses a different frequency, and I was unable to make it work with my VR241 monitor. The outputs from the CGA card are TTL levels, and must be reduced to the approximately 1V P-P levels of the VR241 inputs. Also, a separate sync signal needs to be supplied. Since the Rainbow generates an RGB analog signal, the sync signal can be (and is) included in the Green signal. CGA cards generate a separate sync signal. The pinouts of the DB9 connector on the CGA card should be: 1 Ground 2 Ground 3 Primary Red 4 Primary Green 5 Primary Blue 6 Intensity 7 Mono Video 8 Horizontal Retrace 9 Vertical Retrace Connect a 220 Ohm resistor to each of the color output pins of the DB9 connector on the back of the CGA card (pins 3, 4 and 5). Now connect three 200 Ohm resistors to pin 6. Join the other (free) end of each of the 3 resistors to the free ends of one of the resistors connected to pins 3, 4 and 5. Join wires to these three joins and they now become the Red, Green and Blue inputs to the VR241 color monitor. The necessary sync is provided by simply connecting the composite video out from the CGA card to the sync input of the DEC VR241 monitor. This level is already correct at 1 volt P-P. By using very small resistors, the whole network can fit inside the case of the DB9 connector. DB9 Connector ------------------------------- Blu Grn Red .Gnd. 5 4 3 2 1 o o o o---o o o o o 9 8 7 6 Intensity ------------------------------ SCHEMATIC TTL 5V input Pin Function 1,2 Gnd o--+-+-+ 220 Ohm +--+--+--o Gnd Shield 3 Red o--O-|-|--/\/\/\/\----------------+-|--|--O--o R ~1V output 4 Green o----O-|--/\/\/\/\----------+-----|-|--O-----o G 5 Blue o------O--/\/\/\/\---+------|-----|-O--------o B | | | | | | These 3 resistors \ \ \ between / / / 180 and 270 Ohms \ \ \ (220 Ohms works) / / / \ \ \ 6 | | | Intensity o--------------------+------+-----' External RCA phono socket Composite Video output (1V pp) o---------------------o Sync Connect this set up to a DEC VR241 color monitor and it should provide 16 colors from an IBM PC color graphics card. Set the SYNC switch on the VR241 monitor to the EXT position. 220 Ohms was determined by measuring the output voltages with an oscilloscope using a 75 ohm load. If you vary the resistors, then the voltage will vary. This is not too important within certain limits (given that the cable is short). You can vary the values to change the colors and intensity, depending on the monitor used and your own personal preferences. And, here's a little batch file to check out your colors after you get it all set up. : DOS batch file to test all 16 colors : Replace the *'s with an : Note: In SideKick type ^QA*^P^[gn echo off echo *[0mForeGround Colors. Color guns on. echo I R G B echo *[30m *[37mBlack (white) 0 0 0 0 echo *[31m Red 0 0 0 1 echo *[32m Green 0 0 1 0 echo *[33m Yellow (IBM Brown) 0 0 1 1 echo *[34m Blue 0 1 0 0 echo *[35m Magenta 0 1 0 1 echo *[36m Cyan 0 1 1 0 echo *[37m White 0 1 1 1*[1m echo *[30;1m Grey 1 0 0 0 echo *[31;1m Bright Red 1 0 0 1 echo *[32;1m Bright Green 1 0 1 0 echo *[33;1m Bright Yellow 1 0 1 1 echo *[34;1m Bright Blue 1 1 0 0 echo *[35;1m Bright Magenta 1 1 0 1 echo *[36;1m Bright Cyan 1 1 1 0 echo *[37;1m Bright White 1 1 1 1*[0m :End