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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But I thought gate like those didn’t need to be protected. Which I have interpreted as: It is likely that the output remained in a high-impedance state, so the LED did not light.
This is clearly what I am expecting. A tristrate output can have 3 different states: Email Required, but never shown.
I have tried other gate 19 with 15, 13, 11 and I have the same behavior. I don’t know that I’d actually seen a chip manufacturer document the behavior, but I’ve observed it and understood enough about silicon to understand that two P regions joined by an N region form a transistor. I’m trying to understand how the 74LS works.
I have the feeling that I have understood the schematic, but the fact is this is not working. Texas Instruments discusses some of these results of reduced voltage power supply voltages to ICs, in this short ” Designing With Logic ” document. JvO 2 Sign up using Email and Password. Note the invertor symbol tiny o ring at the control gate connected to 74ks241 1; you must pull pin 19 high to activate, and pin 1 low to activate.
Pins 1 and 19 of the LS control this state for the buffers inside the chip. It is not guaranteed to operate at 3. SE topics where powering devices via other pins, instead of the power pins, caused unexpected behaviour: But my led at pin 18 just glow dimly and never change state, no matter if pin 2 is high or not connected.
Do you understand what a buffer is and why we use it?
What does “put a led on the 3 output pin” mean? 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. These ‘G’ inputs must be activated in datashset to have the buffers connected to them pull their outputs low or high, depeding on their input.
This is not unexpected, since you didn’t power the IC via its power pins for this test. I didn’t put any resistors on the input. Then i wired the 19 and 17 pin with 3. Therefore any results you get using a power supply of 3. When you connected [3. Post as a guest Name. Then [you connected 3. In the first two instances the output is actively pulled low or high using a transistor; in the disconnected state, neither transistor is activated.
Home Questions Tags Users Unanswered. 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 was wondering if I didn’t have broke my chip because I don’t have protected the input gate, but it wasn’t asked in the schema. For some reason, this isn’t working on my circuit. SE topics where powering devices via other pins, instead of the power pins, caused unexpected behaviour:.
Mr Bonjour 1 2 Therefore it is dataxheet no surprise that when you did connect pins 17 and 19 to Vcc, the LED stayed lit. Why is my microcontroller passing a current through it when not connected?
Which I have interpreted as being: Another issue I’ve observed is parts that behave as though pairs of pins are connected via PNP transistor, such that excessive voltage on one will cause the device to source current into the adjacent pin. Your explanation “two input are high” sounds more like the definition of an AND gate.
The LED being lit is not a surprise. I would have guessed the current gain was more than 0.