Re: [CAD_CAM_EDM_DRO] Re: TTL to HTL signal conversion

On Friday 06 February 2004 04:13 pm, Roy J. Tellason wrote:

> On Friday 06 February 2004 01:49 pm, birdmanure wrote:
> > You can do a search on RS-232 bus interface drivers. RS-232
> > drivers are designed to work at up to +/-25V. The older
> > 1488/1489 (and I believe 75451/75452)
>
> That's 75188 and 75189.
>
> > chips require +/-12V power supplies,
>
> Only the driver, the receiver runs off a single +5v supply.
>
> I'm not sure if these would work. A minimum "valid" level for RS232 is 3
> volts, above or below ground, and the region in between, where zero
> volts is, is technically undefined by the standard. Which may not mean
> this won't work, I haven't actually tried seeing what the receiver chip
> will do under those circumstances. I'm also not familiar with the output
> specs of HTL, what constitutes a "low" output on one of those parts? I
> sure as heck don't have any data on them handy...
>
> http://docs.yahoo.com/info/terms/

With the 1488/89 pair the receiver needed a pullup to +5 to accept a TTL
input. The negative swing was not needed. I learned this years ago when
investigating a "TTL compatible" device. At the time I found it "interesting"
that the transition point for the receiver was +3 volts; +3, -12 didn't
matter other than the closer to -12 the more noise immunity. Back in ancient
times the Motorola databook actually had a schematic of the chip <g>.
--
Keith Bowers - Thomasville, NC