Blinking and underlined characters for dosbox

[luckiejacky]

I understand that the hercules card (MC6845 chip) use a specialized circuitry to render an underlined and blinking character under mode 7. I would like to know how it is possible to emulate it in dosbox? I mean programmatically.
At least I need to find a "map" or image of how the screen would look like and try to imitate. And Just couldn't find any.
Any ideas?
Thanks
Jack