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Whatever will be the value either 0 or 1, it will not affect the output. Vcc is available by default in proteus. Can i build a down counter with 74ls90? Loading Comments Email Required Name Required Website. Pin 2 is used as a reset pin in the IC.
It will show the maximum value on the output. It will use with the Pin 3. Pin 3 is also used as a reset pin in the IC. So, what am I missing? How is this chip supposed to work correctly? Why does grounding the input, and applying Vcc voltage to QA iterate the counter?
I'm hoping I'm just missing something obvious. Mixing logic families is generally not a good idea. A lot of parameters to consider to ensure compatibility. Then there is MECL which is another entirely different breed. A cap to VCC in series with a resistor to ground.
I'd think they would show a power on reset circuit in the data sheet, but They won't live a long time with 7 volts, Too much dissipation, stick with 5V. In what manner are you generating clock.
A switch, a push button??? To work properly the clock has to be clean, with a single positive going leading edge. If not it will quite possibly increment several counts with each "clock". Logic families of old had very specific parameters that needed to be met if you were going to have good results.
You could use a square wave generator or pulse generator for a clock source, but be sure the signal you apply to the ICs compatible with their requirements.
Raising the power supply voltage to 7 volts to get more out of the LS chip also raises the input voltage requirement of the chip so nothing is gained. You can make it work with a supply side switch if the resistor to ground is low enough resistance. Consult the data sheet to find out the input current at the recommended low input and use Ohm's law. As mentioned, the clock signal has to be clean.
The IC is more than fast enough to count the bounces that the switch contacts make when they close and open. Some switches with mercury wetted contacts are clean enough if you can get one and it is suitable in other respects, like size and mounting position.
If you want to use an ordinary switch, a debouncer is required between it and the counter. Your circuit doesn't show any power supply bypass capacitors. Omitting them can cause all sorts of strange behavior. Jim Mueller Who's that swimming in the punch bowl? It's Walter Wart, the freaky frog! These chips are very sensitive to "glitching". Leads as short as possible.
That 1K pull-down resistor ain't gonna do it! Needs to be dropped to ohms. Better still don't use pull downs on TTL. Only pull ups. That mechanical switch will be noisy, and generate a bunch of pulses for each depression. Kit has been superceded by a new version. The automatic reset makes the counter to start from 0 and end at 9 in decimal. In IC we have four reset pins from which we can enable the counter by activating specific two pins. In this section working of will be explained.
There are two clock pins and they will be used to change the output state. The reset pins are control through AND gate. The IC comes with 4 reset pins, two clock, and 4 output pins.
When we are going to use the IC then we need to understand the reset pins first. These four reset pins will be used to control the output. These four reset pins will come up with multiple 16 combinations but in some combinations, there will be fixed output. The First clock pin Pin 14 will be used to give the clock input signal to the IC.
But always keep in mind the concept about the reset pins otherwise IC will give some random value or there will be no output. Here the full functional circuit. Whenever we give the pulse the IC will give the output in binary form. Every binary form will represent a decimal number.
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