Shift Register not working
tpw_man
Posts: 276
First of all, I am new to the Parallax Forums. 
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
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?▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
I am 1010, so be surprised!
Post Edited (tpw_man) : 1/27/2008 11:37:24 PM GMT
Comments
Leon
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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle
Post Edited (Leon) : 1/27/2008 8:40:42 PM GMT
The 74 HC nnn will work fine
The 74 LS nnn will most likely not.
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I am 1010, so be surprised!
Post Edited (tpw_man) : 1/27/2008 9:03:19 PM GMT
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!
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
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I am 1010, so be surprised!
Post Edited (tpw_man) : 1/27/2008 11:37:51 PM GMT
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.
-Phil
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I am 1010, so be surprised!
Post Edited (tpw_man) : 1/27/2008 10:58:09 PM GMT
(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.
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