74hc14 vs 74hct14

[slp_prlzys]

first off, i'm still in the understanding of ohm's law
please be kind

I am experimenting with dc motor using
pwm on a pic18f452 coding in picc, I am
using L298n Dual H-bridge laid out in parallel
to boost current handling, basically I setup
the L298n to use both h-bridge just for one motor.

on first run everything seems working fine,
I could alter the duty cycle and the motor could
forward and reverse as intended(btw. the setup
is using so called "locked antiphase" I'm still digesting it
myself but a search would give you plenty of hits.
Basically with this setup a duty cycle of 50% does
not move the motor, up to 100% motor move forward,
down to 0% reverse.)
then the next day I tried run it again, but I blew up
both 74hc14 and the L298n, I'm not quite sure but
I think it was caused by the capacitor that I have in PSU
which I didn't realize 'till later that it was in parallel with
the one I have in the L298n board.(tho I'm not sure what
effects of parallel caps). I had replaced both chips
and the L298n is working again this time no caps on the PSU
just the hbridge board.
Now to my ? ...due to novice(ness) I bought
74hct14 instead of 74hc14, they seemed to be identical,
except for some that I don't understand yet the problem
is I can't do reverse on my setup it's always forward
with duty cycle 0% no move to 100% forward move. I scavenged
a 74hc14 and now all is the way it should be.
could any1 enlighten me why the antiphase doesn't work
with the HCT, but works with HC version of 7414.

TIA
(sorry for long post)
I'm using 20Khz PWM if the question arise
also using a surplus CMC- ME3515 servo for
the experiment.
PSU 25v DC w/out caps, 37v with 1000uF caps

edit: I had to remove the L298n layout,
I just looked back to the datasheet, and I just
realized I didn't put pin1 &15 in parallel, so
I should use only one sense resistor.

[Al_The_Man]

The basic difference HCT are designed to work at TTL level inputs (5v) and HC are CMOS level rated inputs (15v).
Al

[pminmo]

Clarifying some, the HC needs a higher input voltage to represent a high, rule of thumb GT 50% VCC, HCT on the other hand will typically see an input high at 1.6V. So running a 5V VCC, a voltage on an input of 2.1V the HCT will act on that as a HI, and the HC will act on it as a low. Plus, HC works at a more open 2V to 6V vcc.

[slp_prlzys]

thanks for the time guys,
another one that goes to
my knowledge bin.

I have to admit that this experiment
of mine will be just that an experiment.
after weeks of googling led me to
believed that servo control is one complex
project (atleast for me), but I'll just keep
working on it accepting the fact that
I won't be able to finish it,not enough brain power to do it
just so I'd pick some knowledge in the process.


thanks again.