Uploaded May 2017 | Updated September 2026, 2 weeks ago
I was at the local retro computer meeting the other day and one of the guys was trying to interface the CGA video output to a VGA monitor with a Chinese 15kHz to VGA upscaler. It did work, but only if the picture didn't change. Otherwise the sync would drop out.
I decided to have a go at making my own scan doubler. This one needs 2kB of 4-bit RAM (provided in the FPGA) to store a single line, which is then output twice in succession at double the speed. This gives a signal that's compatible with VGA.
There is some sampling jitter, visible when I zoom in, because I'm running the board at 50MHz and the sample rate for CGA/EGA is 14.3181MHz. If I try it at a multiple of 27MHz I might have more luck.
The machine is an NEC PowerMate 1 Plus 80286 with 4MB RAM and a 40MB hard drive. It has an EGA graphics card.
I'm using a FleaFPGA development board from www.fleasystems.com, which is an excellent little board for this sort of thing.
I was at the local retro computer meeting the other day and one of the guys was trying to interface the CGA video output to a VGA monitor with a Chinese 15kHz to VGA upscaler. It did work, but only if the picture didn't change. Otherwise the sync would drop out.
I decided to have a go at making my own scan doubler. This one needs 2kB of 4-bit RAM (provided in the FPGA) to store a single line, which is then output twice in succession at double the speed. This gives a signal that's compatible with VGA.
There is some sampling jitter, visible when I zoom in, because I'm running the board at 50MHz and the sample rate for CGA/EGA is 14.3181MHz. If I try it at a multiple of 27MHz I might have more luck.
The machine is an NEC PowerMate 1 Plus 80286 with 4MB RAM and a 40MB hard drive. It has an EGA graphics card.
I'm using a FleaFPGA development board from www.fleasystems.com, which is an excellent little board for this sort of thing.
