From a textbook:

"The parity bit is chosen so that the total number of 1's in a coded frame is even. We say that the coded frame has even parity."

From a basic explanation in a Web site:

"Computing parity involves counting the number of ones in a unit of data, and adding either a zero or a one (called a parity bit) to make the count even (for even parity) or odd (for odd parity).

For example, 1001 is a 4-bit data unit containing two one bits; since that is an even number, a zero would be added to maintain even parity,...."

To my surprise, :!: from AN 160 from Linx Technologies:

"A parity check is accomplished by adding all of the '1's in a string of bits. For even parity, if the number is even, then the parity bit is set, otherwise it is not."

(Bold formatting is mine)

Comments anyone?

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Agustín Tomás
In theory, there is no difference between theory and practice. In practice, however, there is.

 

That last bit can only be true if they are talking about a status bit in a status register. A status bit can be chosen to indicate either even or odd parity.

 

Sorry, I should have added the whole text. The AN it's not mentioning any status register but the byte to be xmitted.

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Agustín Tomás
In theory, there is no difference between theory and practice. In practice, however, there is.

 

Are you planning using a parity bit for something?, you should be aware that it offers the least amount of checking possible - and isn't really worth bothering with?.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

No. Hamming code 7,4 instead, complemented with repetition (thrice) followed with majority vote. Could sound overkill for my IR link between two PICs but they are easily implemented in software.

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Agustín Tomás
In theory, there is no difference between theory and practice. In practice, however, there is.

 

As you're writing both ends of the link, then you can deal with the parity bit exactly as you wish - but it seems rather pointless?.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

Sure. I'am the 100% of the development team, only using parity check to build the 7,4 Hamming code, later complemented as described.

BTW, NIgel, could you suggest a simple / practical way to check the error correction part :?: keeping in mind it is a non-outdoors bot where the "one way" IR link between the brains and each leg is aimed basically to control motors.

Gracias.

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Agustín Tomás
In theory, there is no difference between theory and practice. In practice, however, there is.

 

You might try sending a checksum - it doesn't have the capability of correcting errors, but it is a good way of showing an error exists.

I'm presuming you're continuously sending data?, the robot should enter a 'safe mode' if it doesn't get valid data within a certain time - this means it will 'fail safe'.

However, because you can continually send data (which will mostly be the same), missing the occasional byte or two doesn't really matter.

Your TV remote does no error checking, does that work well enough or not?.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

The brains will tell the legs when to start / stop / reverse. No continuous emision planned. Too much power to save in that way!

No TV remote used, just an IR link based in the SIRC protocol from brains to legs.

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Agustín Tomás
In theory, there is no difference between theory and practice. In practice, however, there is.

 

In that case I suggest you use transceivers and a two way link!.

I meant on your TV! - that works fine doesn't it?, and no error checking!.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

Oh, yes. You are right :!: There is hope after all...

Thanks for your time and good disposition.

Sure I will post the outcome.

__________________
Agustín Tomás
In theory, there is no difference between theory and practice. In practice, however, there is.