it means that each output pin has a transistor with the collector being connected to the pin..
open collector outputs can sink a lot more current than standard TTL outputs..

 

But that's not their main reason!. It's so it can be pulled higher than TTL voltages by a pullup resistor, or multiple outputs can be ORed together with a simple pullup resistor. It's a very versatile output, for some purposes far better than normal TTL outputs, but for others not as good, mostly it's used to interface between TTL and something else.

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

 

Alsalm alaycom
First of all I want to thank you for your efforts
I want to ask about pic 16f877a programmer is it the same of 16f877 and I wounder if you could help me to get its schematic.
and whate about programmers types like JDM programmers or PIC burner whate the difference between them and which one is recommended

 

The difference is the software,the hardware for the 877 and 877a is identical.

Never heard of PIC Burner, but JDM's are the most unreliable programmer there is.

I would strongly suggest you get a PICKit2 or a clone.

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

 

Pic burner is another LPT port programmer with external power supply. One design with this tile was published in Electronics For You magazine In India.

__________________
Regards,
Sarma.

 

alsalam alaycom

what is the recommended software for each type ?

why JDM programmers are unreliable ?
I was going to make one

Why you prefer them ?
How could I get there schematics
they are not in winpic800 hardware list . what is the software suggested ? .

Thank you and sorry for asking tooooooo .

 

Most software will do both, it would be rare to find one that didn't.

Because they rely on the PC seriel port exceeding the RS232 specification.

Because they are MicroChip supported, they get new devices added automatically, and work direct from MPLAB.

As I said above, they work direct from MPLAB, or the PICKit2 software.

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

 

I'll chime in here...

The JDM and all those other old programmer designs are pretty much defunct now.
They mostly have interface problems, timing issues and really don't like modern PC hardware, they had their place and time, but no longer. If I desperately had to build a programmer to burn a one off device out in the sticks somewhere, I may well put together something like a JDM or PicPro etc with a couple of transistors and resistors etc. It won't be particularly reliable, but may get the job done at the time.

The value in a decent programmer cannot be understated. Whether you choose a Microchip PICKit2, a clone of some sort, or a professional programmer like the Xeltek that I have matters not. What matters is that the programmer is consistent and reliable, allowing you to concentrate on what you want to do with it, rather than wondering if a device didn't program because the serial port doesn't quite cut it, or the programming voltage fluctuates just enough etc. A decent programmer also has regular support from both the manufacturer and the community and may even have added features like a small logic analyser as in the case of the PICKit2 et al, or a logic chip tester like my Xeltek has.

If the genuine Microchip PICKit2 is too expensive for you, look into the Junebug from Bill at Blueroom, or a straight PICKit2 clone from Sure Electronics. If I were to choose between those, I would have the Junebug on account of it's added features, however both are reliable and consistent programmers, have good ongoing support and features and will allow you to get into your project immediately.


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