74LSN from Fairchild Semiconductor. Find the PDF Datasheet, Specifications and Distributor Information. 74LSN Datasheet, 74LSN PDF, 74LSN Data sheet, 74LSN manual, 74LSN pdf, 74LSN, datenblatt, Electronics 74LSN, alldatasheet. These 8-bit shift registers feature gated serial inputs and an asynchronous clear. A low logic level at either input inhibits entry of the new data, and resets the first.
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The register was clocking multiple times because the clock signal wasn’t enough clean. So I added a schmitt trigger between the raspberry pi and the register clock input, and now it shifts exactly the number I want. A Low power Schottky input typically sits at about 1. Cleaning the pulse up with a Schmitt trigger got it working, but is masking the real problem – you Pi’s GPIO line is either not being controlled correctly by your program, or it’s blown up.
Take a peek at the data sheet. This chip can’t drive the kind of current you want it to. Thus exceeding operating conditions, all bets are off. You likely have reflections on your 74,s164n line, causing it to be treated as multiple clock pulses.
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Do you have an oscilloscope? You are probably getting multiple pulses instead of just one.
Or, the pulse has a ragged edge s and the 74l164n actually clocking several times. You might simply have a logic level compatibility issue between Pi and the LS inputs.
Might be missing decoupling capacitors too. FiddyOhm Reading the datasheet here, I can’t find an issue with the logic levels. The thresholds are 0. See this answer to a previous topic, for more info.
You have an unexplained 1V offset. Perhaps this has something to do with your problem. Finding out where that offset comes from should be the absolute first priority here. Thanks for all your advices and suggestions, have a nice day. I know there is a pull down and a pull up in the ddatasheet pi when you configure the GPIO as input, but is there a pull down when you are in output mode? Output mode is push-pull with at least 2mA sink adtasheet.
I use leds to see what happen. In real I will put mosfets to control a big led board. Negative seems to indicate source current, and positive sink current. You should test with the FETs in place. You might even need to replace the shift register, but probably not. Better yet, JamesMagnus, you have a scope.
Just disconnect the LEDs and use the scope to check outputs. That’s a good guess, but the recent oscilloscope pictures posted after your answer looks pretty clean. That’s pretty far fetched, given the frequencies involved.
Looks pretty clean but you need to zoom way in to know for sure. Also, why does the daasheet only show 2Vpp in one picture?
The measurement or what I think is the measurement number in all the screen shots says 3. Have you ever had bounce problems using a dagasheet microcontroller DIO, especially at low freq? Hasn’t ever happened to me.
74LS – 8-Bit Shift Register Ser In/Para Out
When the asker is sourcing more than the chip can do by more than a factor of 10, I’d look there first. Sign up or log in 774ls164n up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown.