Hi Harold!

I was enlighten by your descriptive definition,
Somehow I got confused with the open drain.
Is there a graphical representation to facilitate understanding?

Also, I'll add some terminology:

Pull-Up resistor, or simply pull-up?
Pull-down

Thanks

Don
Philippines

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Harold Hallikainen
Sent: Friday, June 04, 2004 12:43 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: TERMINOLOGY

OK, I'll jump in here. Just finished teaching a class on digital
electronics at Cuesta College, San Luis Obispo, CA.

I believe a lot of the terminology is based on conventional current flow
(instead of electron current flow), so we assume current flows "down
hill"
from positive to negative, or from more positive to less positive, etc.

Source current is current conventional current leaving the device. For
example, if we have a PIC pin that is high (+5V) and load it with 1k to
ground, the PIC is sourcing 5mA. Most PIC pins can source 25mA.

Sink current is how much current the pin can "sink" or pull down. If,
for
example, we have a 1k resistor between a pic pin and +5V, and the pin is
low (0V), we have 5mA flowing into the pin. The pin is sinking 5mA. Most
PIC pins can sink 25mA.

An open collector (bipolar transistor) or open drain (FET) output is one
that can sink current but not source current. Open drain outputs are
often
connected in parallel and have a pull-up resistor somewhere. When any of
the outputs go low, bus is pulled low. This is often used for interrupt
lines. Any device can pull the interrupt request line low. The processor
then polls the devices to see which pulled it low.

For a little more basic electronic theory, see
http://kauko.hallikainen.org/rw/theory/

Good luck!

Harold

> Ok, I'll take a shot at these.  The terminology gets pretty confusing
> sometimes.  As for the best place to look?  Probably an EE book.
>
> -Sink current is how much current you can sink, or how much you can
pass
> through that portion of the circuit.
>
> -Source current is how much current you can source, or how much
current
> that portion of the circuit can pony up.
>
> -Open drain means that it goes straight to ground at some point.
> Usually sooner than later.  :-) .  In other words, you would be able
to
> sink a larger amount of current through that portion of the chip than
> one that had a specificed sink current.  TYPICALLY.
>
> Someone jump in if I screwed anything up, but that should be pretty
> accurate.
>
>
> Shawn Wilton
> Junior in CpE
> MicroBiologist
>
> Phone: (503) 881-2707
> Email: shawn@black9.net
>
> http://black9.net
>
>
> techy fellow wrote:
>> Hi All,
>>
>> Am new to electronics, can someone kindly explain to me or direct me
to
>> somewhere I can do my own reading on the following commonly used
terms
>> for MCU;
>>
>> - Sink Current
>> - Source Current
>> - Open Drain
>>
>> Thanks in advance.
>> Davis
>>
>>
>>
>>
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