In message , Bill in Co
writes:
Lostgallifreyan wrote:
[]
Some equipment uses 'TTL' levels (0=0.3V and 1=4.7V)

Just FYI, the logic levels are a bit off here. Actually, the TTL logic
levels a

Input: 0 to 0.8 V is a logic low input, and 2.2 to 5V is a logic high
input.
Output: 0 to 0.4 V for a logic low output, and 2.6 to 5V for a logic high
output.


There's even more to it:
The levels Lg describes - 0 near 0V, and 1 similarly near +supply - are
CMOS levels (and CMOS , at least 4000 series, doesn't have to run on
5V). TTL was/is based around a threshold (with margins) that is _not_
half-supply voltage, as you have correctly shown, but instead around
1.2V. But even within TTL, there are variations: whether it's the
military (54xx) series or the commercial (74xx), let alone all the
various families (plain, L, H, S, LS, ALS, AS, F, ...), though they're
all supposed to be interoperable at least with a fanout of one.
--
J. P. Gilliver. UMRA: 1960/1985 MB++G.5AL-IS-P--Ch++(p)Ar@T0H+Sh0!:`)DNAf

In a time of drastic change it is the learners who inherit the future. The
learned usually find themselves equipped to live in a world that no longer
exists. -- Eric Hoffer (quoted by Elsie McGill , 1997-6-1).