What's wrong with my circuit ? Why it will start from 90 and not 00?

 

hi 5411,
The 74Ls192 is a parallel load IC, ground pins A,B,C,D.
Also the Load pulse signal should have small delay after switch ON.
E

 

hi 5411,
The 74Ls192 is a parallel load IC, ground pins A,B,C,D.
Also the Load pulse signal should have small delay after switch ON.
E

i had tried to pin ABCD to ground but still occur the same problem and i need to use a 555 timer to make the load delay ? Please teach me.

 

hi,
You could use a resistor in series with a capacitor, connected across the +5V to 0V lines.
The junction of the R and C would be connected to the /Load pin.
Values would be approx 4k7 and 100nF.
Try that on your Simulation.
E

 

Any sequential logic device (flip flops, counters, registers, memories, etc.) will hold unknown values at power-up. With a BCD counter this can include values not normally part of the sequence (1010 through 1111). The only way to deal with this is to load or clear the device after power-up.

A simple RC circuit on the reset pin will probably work OK but it is not a good power-on reset generator because it will not work reliably after a short power drop. Good reset generators are surprisingly complex.

 

hi ebp,
One way to overcome the supply 'brownout' problem is to bypass the resistor with a diode.
Eric

 

The diode definitely helps, but it still isn't adequate for critical aps. The diode will also help prevent excessive current through input protection diodes.

I have some D-Link Ethernet switches that have a bad habit of not resetting properly after a brief power drop.

There are POR ICs that cost more than microcontrollers!

 

Any sequential logic device (flip flops, counters, registers, memories, etc.) will hold unknown values at power-up. With a BCD counter this can include values not normally part of the sequence (1010 through 1111). The only way to deal with this is to load or clear the device after power-up.

A simple RC circuit on the reset pin will probably work OK but it is not a good power-on reset generator because it will not work reliably after a short power drop. Good reset generators are surprisingly complex.

how can i load or clear the device after power-up?

 

hi heng,
You could add a Clear and Load switch and manually Clr/Ld after switch On, which would not help in the fail/restart of the power supply.
It is possible to add extra logic IC's that will create Clear and/or Load pulses at power up and power brown outs, the complexity of the circuit depends upon the projects fail safe specification.

I have used the R/C/Diode Reset as a stand alone network, also with added IC's, as the specification required, with no reported problems.

E