Lpc2000

Does anybody know if the UART TX line on the LPC2129 is capable of supplying
2.2mA, as I need it to drive an optocoupler for isolation

Cheers

Andy

--- In lpc2000@yahoogroups.com, "Andrew Berney" <amb@...> wrote:
>
> Does anybody know if the UART TX line on the LPC2129 is capable of supplying
> 2.2mA, as I need it to drive an optocoupler for isolation
> 
> Cheers
> 
> Andy
>

Hi,
I haven't got the datasheet right for this part.
If you have one you may search there for "IOH" and "IOL" in "Static characteristics" section.
Most likely the minimum values for these parameters will be "-4 mA" and "4 mA" accordingly, as for LPC2106 and LPC2148 for example.
Well, the short answer is "yes".

Regards,
Max

Andrew Berney wrote:
> Does anybody know if the UART TX line on the LPC2129 is capable of supplying
> 2.2mA, as I need it to drive an optocoupler for isolation

Yes, I have implemented isolated coms using HP2531s via 220R resistors 
without any problems. Vol/Voh are not as relevant as Iol/Ioh when 
driving leds and optos. The values given in the datasheet of 4ma just 
means that you can draw that much and still have the output voltage 
within logic levels *if* you were also driving other logic inputs.

  In your case it doesn't matter if the voltage is not at a logic level 
as long as it supplies the current required (within limits). CMOS 
outputs are very forgiving when driving low-resistance loads, just don't 
expect it to maintain logic highs and lows if you push it.

*Peter*

> Yes, I have implemented isolated coms using HP2531s via 220R resistors
> without any problems. Vol/Voh are not as relevant as Iol/Ioh when
> driving leds and optos. The values given in the datasheet of 4ma just
> means that you can draw that much and still have the output voltage
> within logic levels *if* you were also driving other logic inputs.
>

What is maximum baud rate achievable in isolated RS232. We are unable to get
more than 38400.

Best Regards,

Mukund Deshmukh.
Beta Computronics Pvt Ltd
10/1, IT Park, Parsodi,
Nagpur-440022
Cell - 9422113746

At 18:29 27.04.2006 +0530, you wrote:
> > Yes, I have implemented isolated coms using HP2531s via 220R resistors
> > without any problems. Vol/Voh are not as relevant as Iol/Ioh when
> > driving leds and optos. The values given in the datasheet of 4ma just
> > means that you can draw that much and still have the output voltage
> > within logic levels *if* you were also driving other logic inputs.
> >
>
>What is maximum baud rate achievable in isolated RS232. We are unable to get
>more than 38400.

That depends very heavily on the optocoupler you use; some of them can be 
used for 9600 baud only, some are very fast. Have a look in the specs of 
the couplers (I currently do not have a recommendation for you).

Herbert


>Best Regards,
>
>Mukund Deshmukh.
>Beta Computronics Pvt Ltd
>10/1, IT Park, Parsodi,
>Nagpur-440022
>Cell - 9422113746
>
>
>
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[Non-text portions of this message have been removed]

Mukund Deshmukh wrote:
> What is maximum baud rate achievable in isolated RS232. We are unable to get
> more than 38400.

That depends on your choice of opto, drive and load resistors more than 
anything else, these are your limiting factors. Assuming the opto is 
fast enough and sensitive enough (Tplh/Tphl and CTR) then you should 
drive the optos as hard as you can as you will need as low a value 
collector load resistor as possible to achieve a fast low to high on the 
opto collector ...... and so on.

??? That's ok, if you want speed, don't use unbuffered optos, go for 
something with a logic buffers built-in, these are designed for speed.

*Peter*

> That depends on your choice of opto, drive and load resistors more than 
> anything else, these are your limiting factors. Assuming the opto is 
> fast enough and sensitive enough (Tplh/Tphl and CTR) then you should 
> drive the optos as hard as you can as you will need as low a value 
> collector load resistor as possible to achieve a fast low to high on the 
> opto collector ...... and so on.
> 
> ??? That's ok, if you want speed, don't use unbuffered optos, go for 
> something with a logic buffers built-in, these are designed for speed.
> 

Can you suggest some opto coupler for 115200 baud rate?



Best Regards,

Mukund Deshmukh.
Beta Computronics Pvt Ltd
10/1, IT Park, Parsodi,
Nagpur-440022
Cell - 9422113746

--- In lpc2000@yahoogroups.com, Mukund Deshmukh <betacomp_ngp@...> wrote:

> 
> Can you suggest some opto coupler for 115200 baud rate?
> 

http://www.analog.com/en/prod/0,2877,ADuM1201,00.html


Max. Data Rate 	25Mbps


http://www.analog.com/en/subCat/0,2879,767%255F827%255F0%255F%255F0%255F,00.html

Peter Jakacki wrote:
> Mukund Deshmukh wrote:
> 
>>What is maximum baud rate achievable in isolated RS232. We are unable to get
>>more than 38400.

Analog devices makes a product line called iCoupler. It can
be used as a replacement for optoisolators (they're magnetic
isolators). They operate up to may Mbps. Check out this link

http://www.analog.com/en/subCat/0,2879,767%255F827%255F0%255F%255F0%255F,00.html

or Google for iCoupler and it'll show up.

I haven't used this for rs232 links, but I don't see any reason
why it wouldn't work. Maxim also has some isolated parts.

Cheers
Dave