View Single Post
Old 18th Dec 2011, 10:53 pm   #4
No Longer a Member
Join Date: Sep 2008
Location: London, UK.
Posts: 117
Default Re: IMOGen Test Card & Teletext Generator

Thanks, both. Mike, the fiver we agreed is in the post

Originally Posted by dragonser View Post
.....UV erasable eproms would not be fast enough to use ?
The pixel rate is 12MHz so everything has to happen within 83ns. Finding fast enough UV EPROMs is both much harder, and considerably more expensive, than the 70ns FLASH PROMs I'm using. No reason why they couldn't be used if suitable parts were to turn up in a bargain job lot! It's always possible that 90ns UV EPROMs may work, though that's really hoping the spec is generous enough to just about allow it, being that nearly all the accessed addresses are sequential. I've never tried it.

The alternative would be to use slower UV EPROMs in Odd/Even address pairs to allow slower PROM access times, but the multiplexing and data latching requirements add complication, and one of my aims from the outset was to try to avoid having any further logic between the PROM data lines and the DAC. As certain people on here will know, mainly because I'm not smart enough to design it
Parabola is offline