I want to use one of them as input to a CPLD and the others I want to take input from the CPLD so sounds like I should use 4.7K (thanks). If I am going to use the pin as input do you think I still need the resistor or will I need it for both input and output of the pins?
Thanks again.
rtstofer <rstofer@...> wrote:
--- In lpc2000@yahoogroups.com, John Stamos <jstamos111@...> wrote:
>
> Can someone recommend a good resistor value to use for the pullup
resistor?
>
> Much Thanks.
It depends on what you want to do with the pins.
If you want to use them as normal outputs to other logic gates, the
value is probably on the order of 4.7k. The resistor is responsible
for holding a logic '1' on the signal line while driving downstream
components. So, it depends on how many gates you are driving, the
required logic voltage levels, logic input current requirements, etc.
If you want to use I2C then a value around 2.2k would be better - but
that is a value for LSTTL. The proper way to size these is with
reference to the I2C Specification available from Philips.
If you just want to stuff resistors in and not get carried away with
details, use 2.2k and see how it goes.
Richard
>
> Robert Adsett <subscriptions@...> wrote: At 06:36 PM 5/20/06
+0000, jstamos111 wrote:
> >Hey guys,
> >
> >This problem has me completely baffled. Hopefully you can help.
> >
> >I have an LPC2106 running on a board of my own design and am using
> >Keil tools to compile the code. Here's my very short code:
> >
> >void main() {
> >PINSEL0 &= 0x00000000;
> >IODIR0 = 0xFFFFFFFF;
> >IOSET0 = 0xFFFFFFFF;
> >while(1);
> >}
> >
> >The problems when I run this code all IO ports turn on except P0.2,
> >P0.3 and P0.26. Any idea why? I tried looking in the documentation
> >but couldn't find anything specific about these ports not working for
> >IO. I thought maybe the problem was what I had the pins connected to
> >(a CPLD) so I made sure to put the connected CPLD pins as inputs and
> >even disconnected one pin completely and still the same problem. I
> >have multiple boards and it does it for at least two of them.
>
> Well P0.2 & P0.3 are open collector so they'll need pull-ups. See
> http://www.open-research.org.uk/ARMuC/LPC2100Tips.html
>
> P0.26 I don't see anything off hand unless you have JTAG enabled.
>
> Robert
>
> " 'Freedom' has no meaning of itself. There are always
restrictions, be
> they legal, genetic, or physical. If you don't believe me, try to
chew a
> radio signal. " -- Kelvin Throop, III
> http://www.aeolusdevelopment.com/
>
>
>
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