TTL logic and the stamp
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Posts: 46,084
Hello from Gregg C Levine
I'm probably missing the merely obvious portion of this, but here
goes, the tips screens all state that the stamp operates at normal TTL
logic levels. I can see why I should connect those LEDs to the stamp
using those resistors, it protects the stamp, as well as the LED. Is
any sort of pull up, or pull down resistor needed for communicating
with an ordinary TTL gate, such as one quarter of a SN7437? I know I
worked that out, early on, when I bought the first stamp, but I don't
have my notes, or worse, the local archive of this group.
And gentlemen, (and ladies), thank you for answering those questions
regarding the serial questions.
Gregg C Levine hansolofalcon@w...
"The Force will be with you...Always." Obi-Wan Kenobi
"Use the Force, Luke."· Obi-Wan Kenobi
I'm probably missing the merely obvious portion of this, but here
goes, the tips screens all state that the stamp operates at normal TTL
logic levels. I can see why I should connect those LEDs to the stamp
using those resistors, it protects the stamp, as well as the LED. Is
any sort of pull up, or pull down resistor needed for communicating
with an ordinary TTL gate, such as one quarter of a SN7437? I know I
worked that out, early on, when I bought the first stamp, but I don't
have my notes, or worse, the local archive of this group.
And gentlemen, (and ladies), thank you for answering those questions
regarding the serial questions.
Gregg C Levine hansolofalcon@w...
"The Force will be with you...Always." Obi-Wan Kenobi
"Use the Force, Luke."· Obi-Wan Kenobi
Comments
If the stamp output pin is driving a TTL gate, and the stamp pin REMAINS in
ouput mode, and does not enter sleep mode, no external pull up or pull down
should be needed. The Stamp is supplying a discrete logic high or low.
ken
-============
Hello from Gregg C Levine
I'm probably missing the merely obvious portion of this, but here
goes, the tips screens all state that the stamp operates at normal TTL
logic levels. I can see why I should connect those LEDs to the stamp
using those resistors, it protects the stamp, as well as the LED. Is
any sort of pull up, or pull down resistor needed for communicating
with an ordinary TTL gate, such as one quarter of a SN7437? I know I
worked that out, early on, when I bought the first stamp, but I don't
have my notes, or worse, the local archive of this group.
[noparse][[/noparse]Non-text portions of this message have been removed]
an ordinary TTL chip - in general. There may be exceptions however.
E.g. you can configure a stamp pin as input or output and thus you
may want a resistor to protect against programming misstakes which
may cause shorts. Besides this, a particular design might ask for
additional protective or pullup/-down resistors to make it more
robust.
Regards
Adrian
resistors. However, not all TTL is created equal. There is TTL, LS, ALS,
C, HC, and several others. I have used the TTL, LS, and ALS intermixed for
years with no problems.
TTL has what they call fan out. This means that one TTL chip can drive (for
example) up to 10 other TTL inputs. This is the standard, but it is not
always met. I try to not connect up more than 5, as I tend to have high
speed circuits<G>.
Some circuits (or microprocessors) say that they can drive TTL circuitry,
though the circuits themselves are not TTL. Usually this is true. Depends
upon the beast<G>.
I do sometimes add a pull up resistor to TTL to get a fast transition.
DANGER WILL ROBINSON::: Pull all unused sections of a TTL chip up to +5
Volts with a 1 k to 10 k Ohm resistor. Pulling them up, instead of pulling
them down, supposidly uses less power. Not pulling them in any direction
can allow the inputs to freewheel, and I have had strange oscillations
(which got ALL OVER my boards) from inputs not pulled in any direction,
before I understood the need. And, if you need to connect that section to
the circuit later, you can leave the 1 K to 10 k Ohm resistor in place, it
won't hurt anything.
I troubleshoot all my logic circuits with an oscilloscope.
Original Message
From: Gregg C Levine [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=6D8eawIOyBUnqehKoewuRfcfni77TavMRrNkc6A1d7LPrR3du1uA_W9wzuODU1r7dVkMYgLf-q7Ets9jitocImybif3RcCHz]hansolofalcon@w...[/url
Sent: Monday, April 05, 2004 11:31 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] TTL logic and the stamp
Hello from Gregg C Levine
I'm probably missing the merely obvious portion of this, but here goes, the
tips screens all state that the stamp operates at normal TTL logic levels. I
can see why I should connect those LEDs to the stamp using those resistors,
it protects the stamp, as well as the LED. Is any sort of pull up, or pull
down resistor needed for communicating with an ordinary TTL gate, such as
one quarter of a SN7437? I know I worked that out, early on, when I bought
the first stamp, but I don't have my notes, or worse, the local archive of
this group.
And gentlemen, (and ladies), thank you for answering those questions
regarding the serial questions.
Gregg C Levine hansolofalcon@w...
"The Force will be with you...Always." Obi-Wan Kenobi
"Use the Force, Luke."· Obi-Wan Kenobi
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