SN54/74LS • SN54/74LS • SN54/74LS DC CHARACTERISTICS OVER OPERATING TEMPERATURE RANGE (unless otherwise specified). S. b l. P. 74LS Octal Buffers AND LINE Drivers WITH 3-state Outputs SN74S, SN74S OCTAL BUFFERS Details, datasheet, quote on part number: 74LS Texas Instruments 74LS Buffers & Line Drivers are available at Mouser Electronics. Mouser offers inventory, pricing, & datasheets for Texas Instruments .

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This will also cause behaviour which is different from the behaviour when correct power is connected. A tristrate output can have 3 different states: Which I have interpreted as: I didn’t put any resistors on the input. Please show the schematic diagram. Therefore it is also no surprise that when you did connect datashdet 17 and 19 to Vcc, the LED stayed lit. Home Questions Tags Users Unanswered.

If you use a 5V power supply, and make sure this is always connected to the device Vcc and Gnd pins see belowthen you should see expected behaviour. Then i wired the 19 and 17 pin with 3.

A 74LS or any 74LS family part will normally see an unconnected input as a High – you need to connect inputs directly to Ground to input a Low.


By using our site, you acknowledge that you have read and understand our Cookie DatwsheetPrivacy Policyand our Terms of Service. I have put a led on the 3 output pin, in order to test the output.

(PDF) 74LS241 Datasheet download

Therefore any results you get using a power supply of 3. It is likely that the dxtasheet remained in a high-impedance state, so the LED did not light. For some reason, this isn’t working on my circuit.

Mr Bonjour 1 2 This circuit will help: Sign up or log in Sign up using Google.

In the first two instances the output is actively pulled low or high using a transistor; in the disconnected state, neither transistor is activated. Do you understand what a buffer is and why we use it?

Email Required, 74,s241 never shown. Pins 1 and 19 of the LS control this state for the buffers inside the chip.

It is not guaranteed to operate at 3. This is clearly what I am expecting. So here is what I did: I’m trying to understand how the 74LS works.

74LS datasheet, Pinout ,application circuits OCTAL BUFFERS AND LINE DRIVERS WITH 3-STATE OUTPUTS

And when I connect the Vcc pin [ Unfortunately your test is invalid because according datasneet your recent schematic your Vcc supply to the 74LS is only 3. Sign up using Email and Password. Without it, the outputs float. Post as a guest Name. But I thought gate like those didn’t need to be protected.


MrBonjour Try another gate then. Unless you know exactly what you are doing and its consequences, do not apply voltages to the other pins of an IC, without the correct power supply voltage s also being supplied to its specified power pins i. From what I read, if two input are high on a buffer, then the output will be high. I’ve done quite a lot of research since first writing this answer, and with unpowered 74LS devices and an input voltage between 0 V and 5.

I have tried other gate 19 with 15, 13, 11 and I have the same behavior. Why is my microcontroller passing a current through it when not connected? This is not unexpected, since you didn’t power the IC via its power pins for this test. 74ls2411 my led at pin 18 just glow dimly and never change state, no matter if pin 2 is high or not connected.

Texas Instruments discusses some of these results of reduced voltage power supply voltages to ICs, in this short ” Designing With Logic ” document.