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tpw_man
01-28-2008, 03:24 AM
First of all, I am new to the Parallax Forums. http://forums.parallax.com/images/smilies/smilewinkgrin.gif My problem is that I am trying to use a 74LS164 shift register for a scrolling LED display. It does not work with the propellor, but it works fine with a BS2. I suspect it is a logic level problem, but I am not sure. Does anybody know what to do?

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I am 1010, so be surprised!

Post Edited (tpw_man) : 1/27/2008 11:37:24 PM GMT

Leon
01-28-2008, 03:34 AM
Presumably the '164 is powered from 5V. You could try using pullup resistors to 5V on the inputs.

Leon

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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

Post Edited (Leon) : 1/27/2008 8:40:42 PM GMT

deSilva
01-28-2008, 03:37 AM
I don't know what an LC is?!
The 74 HC nnn will work fine
The 74 LS nnn will most likely not.

tpw_man
01-28-2008, 03:40 AM
Thanks for the quick reply!

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I am 1010, so be surprised!

Post Edited (tpw_man) : 1/27/2008 9:03:19 PM GMT

tpw_man
01-28-2008, 03:59 AM
@deSilva
It is 'LS', not 'LC'.

@Leon
470 ohm resistors don't work. Is there a suggested value that would?

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I am 1010, so be surprised!

deSilva
01-28-2008, 04:00 AM
Then it will not work.. take a HC!
--------------------------
Edit:
But I should ask again: What are you doing in the first place? Which supply voltage? Please post a circuit sketch. Leon is right that under certain circumstances you can harm the Propeller when connecting a 5 V output to a Propeller input....

Post Edited (deSilva) : 1/27/2008 9:09:53 PM GMT

tpw_man
01-28-2008, 04:25 AM
My problem is that I am trying to use a 74LS164 serial in/parallel out shift register for a scrolling LED display. It does not work with the propellor, but it works fine with a BS2. The circuits are connected to 5v.

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I am 1010, so be surprised!

Post Edited (tpw_man) : 1/27/2008 11:37:51 PM GMT

Phil Pilgrim (PhiPi)
01-28-2008, 04:38 AM
If you're powering the shift register from 3.3V, a 75HC164 will work fine. If you're powering it from 5V, use a 75HCT164 instead.

BTW, if you're going to post a schematic, please post one that's halfway legible. We're here to help, but runes and hieroglyphics are somewhat out of our realm. http://forums.parallax.com/images/smilies/smile.gif

-Phil

tpw_man
01-28-2008, 05:11 AM
Is the schematic better? http://forums.parallax.com/images/smilies/smile.gif I did it in a schematic editing program rather than drawing it. Can I confirm that I need some sort of 3.3v shift register to interface with the propellor? Anyway, thanks for all the help! http://forums.parallax.com/images/smilies/smilewinkgrin.gif

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I am 1010, so be surprised!

Post Edited (tpw_man) : 1/27/2008 10:58:09 PM GMT

deSilva
01-28-2008, 06:10 AM
I shall try again:
(a) There is no such thing as a 74LC164. Please be more precise.
(b) When you connect this chip to 5 V supply voltage you can take a 74LS164 (but you should get accustomed to the HC chips which are way more practical with the propeller).
(c) The OUTPUT from the propeller can control a 74LS; there is no need for a level shifter.
(d) If - though you do not with that application! - but IF you connect an output from an LS chip to a Propeller input you should include a 1k to 10k resistor to protect the Propeller inputs.

PJ Allen
01-28-2008, 08:03 AM
The datasheet for the 74HC164 states that its operating voltage range is 2-6VDC. As you lower the voltage you decrease the maximum operating frequency, too, which is likely OK for your purpose.

OzStamp
01-28-2008, 08:24 AM
Can anybody remember the Forrest M Simms schematics

His Tandy digital trainer books etc etc were awesome ..
They were available here in OZ at Tandy..20 years ago alway's loved that (HIS) style easy to read..

A bit of nostalgy...
Wander if Forrest M Simms is still alive...?

cheers Ron.. Mel OZ

PJ Allen
01-28-2008, 08:58 AM
http://www.forrestmims.org/biography.html

deSilva
01-28-2008, 09:08 AM
PJ Allen said...
As you lower the voltage you decrease the maximum operating frequency, too, which is likely OK for your purpose.

.. and it's also O.K. for the Propeller. @3v3 a HC chip will run with 30 MHz which is generally faster than an LS chip @ 5V. Whith some effort you can shift out one bit each 50 ns, which comes to 10 or 20 Mhz depending on how you count http://forums.parallax.com/images/smilies/smile.gif