Need help with PropScope

allie

Hi, wondering why, when I put the PropScope Horizontal Dial on 50ns to 500ns scale,
On the Oscilloscope screen at the bottom it shows Time(us) and not Time(ns).
I'd like to measure a square wave signal at 10(ns) and one at 50(ns). With the Time(us) showing I don't want to do damage to the Scope.
Can I measure these to units.

Regards Allie

iseries

Sorry, the scope doesn't measure that low. Best that can be seen is a 200ns pulse that is not very square.

Mike

allie

Thanks for the info. I am in need of a 10 nano second pluse to load 4 data inputs into a 74hc192 counter from a tlc555 timer.
The data sheet for the 192 say's 10ns to set up and load.
I want to check the signal output (tlc555) with PropScope to verify my RC values for the tlc555.
If the ProScope can sample 200ns then I can test this signal.
wondering why does the PropScope display up to 500na if it can not do it.
Can I do damage to the PropScope if I put signals more than 200ns

regards Allie

iseries

No damage will result but display will not be very good. The interface in this case does not match the hardware abilities.

Mike

shooter

it's not pretty but I've always got "close enough" using this and guessing

2/3*Vcc = Vcc * (1- e^-t / (R*C))

which can be rearranged to:
2/3 = 1- e-t / (R*C)
e-t / (R*C) = 1/3
-t / (R*C) = ln(1/3)
t = 1.1*R*C seconds

Clock Loop

allie wrote: »

Thanks for the info. I am in need of a 10 nano second pluse to load 4 data inputs into a 74hc192 counter from a tlc555 timer.
The data sheet for the 192 say's 10ns to set up and load.

Datasheets can be confusing if you are new to them, but im guessing the 10 nano second pulse you quote is the fastest it can go.

I have used Integrated Circuits > 74 Series > 74HC Series chips at VERY SLOW SPEEDS, and they work fine.
What matters is the Pin5, clock up, and Pin4 clock down speeds you are using. And most info on that datasheet shows nothing for the max time....

I think the number you are quoting is the time it takes for the chip to show the result on the output.

DAtasheet shows this..

HC TYPES
Propagation 
CPU to TCU  TYP    10ns
CPD to TCD  TYP   10ns

These chips will run MUCH slower if you need.

I have connected HC chips to buttons/switch and manually clocked things in (but buttons need something called de-bouncing)
But if you are just learning, buttons/switch are not a bad way to go.


If you look at the datasheet notice the pulse width for CPU and CPD have no maximum.
You will probably be fine with a 0.5hz clock rate from a 555 timer going into CPU or CPD
And you can also use 4 switches as the inputs for BCD/BINARYPRESET.

SLOW it all down, so you can understand the logic chips.
That is the great thing about these older chips is they CAN operate slowly.

Then you can use the propscope on the TCU and TCD outputs and also the BCD-BINARY outputs.
And you then DON'T need all of it running at the very max speed it all can go.
A racecar can drive around the track at its max speed, but it can also go so slow you can walk faster than it.

MANY 74HC chips can go very very slow. And that IS GOOD for beginners!
Its how I learned with them.

555 calculators help calculate your pulse you need for the CPU AND CPD inputs, 0.5hz will give you a pulse every 2 seconds!
Try that!

http://www.ohmslawcalculator.com/555-astable-calculator

You might also want a switch on the ASYN PARALLEL LOAD ENABLE input and the MASTER RESET.

You will switch the ASYN PARALLEL LOAD ENABLE to low (0v) when you want to load the number on the inputs for BCD/BINARYPRESET into the counter.

Then you will switch the ASYN PARALLEL LOAD ENABLE to high (5v) when you want to count up or down with a clock on the CPU and CPD inputs.

Once you clock the cpu and cpd inputs (from low to high), you can view the output with the propscope on the TCU TCD and BCD-BINARY outputs.

If you only clocked the CPU or CPD inputs one pulse transition (from low to high), then the outputs should show one number higher/lower than the inputs for BCD/BINARYPRESET which you loaded into the chip with ASYN PARALLEL LOAD ENABLE.

You can reset the chip with a high input on the reset (5v)

Good luck!

allie

Thanks for the info.
I am now using a slower pulse to The PL(parallel Load Enable) pin from a 555 debounce circuit to load the 192.
All works good.


Allie