Help with electronics terms

I'm having a bit of difficulty understanding the following terms:

A "pull up resistor".

[But then I have a bit of a problem when folk say they have "added a load" to a circuit, with a resistor, when I would have said (in my logic) that a restriction had been added. But then like the optimist/pessimist dichotomy, it depends whether you are thinking of the resistor added across a short circuit, or an open circuit.]

And "bit-banged serial" which I assume refers to a serial port on a Pic(axe) or similar processor.

Thanks for any clarification, jack

Reply to
spamfree
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Jack,

I wouldn't try to limit yourself with the way people label technologies. If those labels (words) meant something, you wouldn't be looking for a solution for your own project.

They can't do anything more with what they've been provided, so if you need to create something, don't depend on the limiting boundaries set forth by those who have accomplished done one thing or another.

Over the next 20 years, resistors of every make will go completely extinct, including those previously designed to work with positronic PCs. What are you trying to build?

Reply to
peerdom

G'day, Peerdom. I'm mainly trying to learn. I was once accused of reinventing the wheel -- no, come to think of it, I've been told that several times. Many years ago I started making a pedal radio out of a car generator. Still have the bits. One day I may get it chrome plated and mount it on a jarrah plinth :) At around the same time, I did a course in programming an old CP/M computer with Pascal to do a simple accounting job. I was told not to be silly and to buy an accounting package off the shelf. I thought it was a much more practical effort than my overpaid seniors' effort in writing a similar program in FORTRAN on an old IBM mainframe using punch cards! The only bottom line to all of this wasted effort was that the big boss had some warped idea that anything that came out of a dot matrix printer was gospel. Oh, well!.

I'm again reinventing the wheel, but hopefully learning a lot along the way (again). I want to program picaxe microcontrollers to do all sorts of neat things, and especially datalogging of various measurements and perhaps a keyless front door lock, and maybe a controller for an electric wheelchair. For the moment, I will stick with electrons and the various methods of impeding and encouraging their flow, but thanks for your advice, jack

Reply to
spamfree

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A serial port handles one bit of data at a time by definition being only 'one bit wide'.

The banging refers to handling that port, or making any general purpose I/O behave like a serial port, typically in low-level software (although it need not be) written yourself rather than letting relevent hardware ( a UART for example which may be on-chip) handle it for example.

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Graham

Reply to
Eeyore

This is needed on the output of an "open collector" (or "open drain", etc) type logic gate. Consider the output stage to be a simple switch with one side connected to ground and the other side connected to the output pin. The pull-up goes between the output pin and the power rail, so that the pin will go high when the switch is open. When the switch is closed, the pin is effectively shorted to ground so the output voltage is zero (and current flows through the pull-up).

This means that the serial port operation is done by careful programming of the processor (to get the timig right, etc), as opposed to having a separate chip or circuit within the processor that is dedicated to take care of all the serial port stuff. The dedicated port frees up the processor, allowing it to do something else than babysit the port, so it's handy to have... but of course costs more in dollars and watts.

Best regards,

Bob Masta D A Q A R T A Data AcQuisition And Real-Time Analysis

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Scope, Spectrum, Spectrogram, Signal Generator Science with your sound card!

Reply to
Bob Masta

When you add a resistor to a circuit, there are generally two possibilities as to how it is related to the signal path. The resistor can be added in series with the path, or in parallel to it (making an additional branch). Pull up resistors produce a parallel branch of a signal path to a positive supply, to provide a tendency for the signal voltage to head toward the positive supply, when all other influences (like an open collector transistor that pulls the signal line to ground, when the transistor turns on) turn off. It provides a default, no drive situation, voltage.

Serial communications involve timing bit states so that they follow one another at the baud rate. Programming a port line to produce a serial output is pretty simple, with only a per character permission (handshaking) scheme that controls it. But receiving a serial stream involves syncing to the bit timing to the leading edge of the start bit of each character (in the case of asynchronous serial), and this is usually done with a resolution of 1/16th of the bit time. Writing code that does this process is called bit banging. The alternative is to use hardware that performs all these tasks, automatically, leaving your processor free to do other things, with just an occasional character move into or out of the hardware.

Reply to
John Popelish

Eeyore got this one pretty good.

Think of it as adding a conductance in parallel with whatever the output is. Conductance, being the reciprocal of resistance, means there's "more load" with _less_ resistance across the output terminals.

Typically, "more load" means more current output.

Like Eeyore said, it's just emulating a UART in software/firmware.

Hope This Helps! Rich

Reply to
Rich Grise

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