How to develop a random number generation device

Hmmm, seems like all 0's must be the lockup for an all XOR feedback.

Sorry.

John

Le Thu, 06 Sep 2007 08:54:17 -0400, Spehro Pefhany a écrit:

Does printf work on 7 segments led displays? ;-)

Well it's a bit limited.... it works on a 8x1 character LCD module though!

There's a full list of Modulo 2 Primitive Polynomials (up to 100 bits) in Chapter 7 of "Numerical Recipes in C". Unfortunately this book is now out of print but the college library will certainly have it. My edition is dated 1988.

I would recommend searching through the Microchip website. There you will find articles on Random Number Generators, and details on specific devices that can drive display modules directly. TomCee

Why wouldn't it? Any printf() requires a putchar() function underneath it. You just need to write one that interfaces to a 7 segment display.

My favourite source for this is:

Hope it works for you.

Michael Kellett

Yes, I've done that.

Since he mentions a "module", the chances are that it speaks ASCII anyway. If it's a raw display, he'd need drivers, a little interrupt-driven scan routine that uses a chunk of ram, and putchar modified.

There is one interesting issue with using a 7-segment display with ASCII-oriented routines.. the latter assume that a "." is a seperate character, but they are interstitial on a 7-segment display, which causes a certain amount of hilarity to ensue when dealing with leading zero blanking and such like. The issue does not arise with character-mode LCD displays.

Best regards, Spehro Pefhany

On Sep 7, 5:43 am, Spehro Pefhany wrote: [... Random number gen ....]

No interrupts really are needed. If all this thing does is display a random number, the main loop can look like this:

while Power Is On if The Button is pressed call MakeRandom call NumberTo7Seg end if

for I = 1 to NumberOfDigits DisplayDigit(I); Delay 10mS next I ClearDisplayPorts end while

The fact that the display ports get cleared each time around (ie the LCD or LED gets no voltage) won't matter because the test of the button being pressed is very quick.

The fact that the display is blanked while the button is held down, could be sold as a feature.

XNOR is the all 1s case. That is likely what you thought about.

BTW: If you are making the shift register for such a thing in a micro, it is usually faster to arrange the bits like this:

Byte0: Has bits 0, 4, 8, ... Byte1: Has bits 1, 5, 9, ... Byte2: Has bits 2, 6, 10, ... Byte3: Has bits 3, 7, 11, ...

This way most of the shifting of the bits is done by moving whole bytes. Only the shift into Byte0 needs an actual shift instuction.

Normally we blank the display (turn off at least one set of drivers) before updating, otherwise you'll get visible ghosting since updating the digit and segment drivers is usually not an atomic operation on an

Yes, you could do it that way, but using interrupts is a "set and forget" type of operation, and I would recommend he uses it. If he wants to blank the display between presses, that's easy too.

Best regards, Spehro Pefhany

I don't follow that. One state, all 0's usually, is the lockup. How do you force that to be part of the sequence?

You can add a lockup state detector, a big OR gate or something, and jam in a "1" if the whole register ever gets to the all-0's state, but then the all-0's state is not part of the sequence, because it never happens again.

A maximal-length pr sequence has one sequence of (2^n)-1 states, and another sequence of a single hangup state.

John

It can happen at the startup though. You have to ensure the nonzero initial state.

VLV

Cool! Thanks!

Cheers! Rich

But the state just before lockup *is* the lockup state. And the state just after lockup is the same. Either the register is all 0's, and it's locked forever, or it's some other code, in which case it hopping through the 2^n-1 states, none of which are zero.

XNOR feedback?

So you're just detecting some arbitrary state, and forcing the next state to be zero. Then detecting the zero state 0 and restarting the sequence. Why bother?

John

This app note has an awesome description of just that. It was posted by "MK" without the "http://" part, so probably wasn't clickable:

Hope This Helps! Rich

If you care about fault tolerance you will ensure recovery from a zero state which occurs at any time.

Best regards, Spehro Pefhany