Microcontrolled's recent thread sparked an idea to use one external SRAM per bit plane for video generation. In a nutshell the idea is to encode the entire video stream, including front and back porches and sync intervals, into the SRAM.
Most of the time the SRAMs are in synchronous Dot-Clocked output mode. They can be updated during the vertical sync interval, or by "going offline" for a frame or two to write the full buffer. "Going offline" would allow simple SPIN updates at leisure.
If it works the concept could readily be extended to more color depth. The SRAMS, Microchip 23K256, are about $1 each and available in DIP.
Increasing the horizontal resolution might be harder as it would involve overclocking the SRAM (anyone know if this can be done?). 40 MHz FRAM may be the way to go for that. The choice of 480 horizontal is both to satisfy SRAM limits and allow for large porches for monitors. Its also the horizontal res of the Sharp PSP screen (480*272, Sparkfun etc)
LATEST STATUS - I'll update this line as work progresses -
Proto hardware except driver/amp built, SRAMs talking via Tim Moore's SPI object.
NEXT STEP -
Encode the video signals; test without driver/amp