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LPC2214 questions

Started by Zdravko December 21, 2004

Hello,
I am going to use LPC2214.
I have some questions which are not clear for me in the User Manual. 1) Can I use the not used external memory bus address lines as GPIO
(A0 and A1 are directly mentioned in the UM but the others not)?
3) What are the limiting values of the voltage on the pins when the
3.3V for the external rail is not present(The 1.8V for the core will
be on all the time)?

Thank you very much and Happy Holidays.

Regards
Zdravko




An Engineer's Guide to the LPC2100 Series

1) You can use external memory interface pins as GPIO.
2) You can check max input current of a pin under "absolute maximum ratings"
in the datasheet. Use a series resistor to limit the input current. The
resistor should be low enough not to degrade switching characteristics
because of the I/O capacitances/inductances and high enough to limit the
input current when 5V or whatever the voltage is applied to the input.
Usually the max input current is between 5-10 mA. For instance, a 2K series
resistor would limit the input current to 2.5mA when 5V is applied. Assuming
this is protect the input from a transient condition, you should be fine.
But if the switching speed is high then 2K resistor will drastically affect
rise and fall times and will add propagation delay.
It is totaly up to your application. But the idea is it is not the voltage
that destroys the input but the current.

Kerem

----- Original Message -----
From: "Zdravko" <>
To: <>
Sent: Tuesday, December 21, 2004 11:41 AM
Subject: [lpc2000] LPC2214 questions >
>
> Hello,
> I am going to use LPC2214.
> I have some questions which are not clear for me in the User Manual. > 1) Can I use the not used external memory bus address lines as GPIO
> (A0 and A1 are directly mentioned in the UM but the others not)?
> 3) What are the limiting values of the voltage on the pins when the
> 3.3V for the external rail is not present(The 1.8V for the core will
> be on all the time)?
>
> Thank you very much and Happy Holidays.
>
> Regards
> Zdravko >
>
> Yahoo! Groups Links



On 21 Dec 2004 at 9:41, Zdravko wrote:

>
>
> Hello,
> I am going to use LPC2214.
> I have some questions which are not clear for me in the User Manual. > 1) Can I use the not used external memory bus address lines as GPIO
> (A0 and A1 are directly mentioned in the UM but the others not)? 3)

Yes you can, but you must be careful. You cannot arbitrarily choose if
a pin is an address line or GPIO. You can for instance choose to use the bottom
8 lines as address lines and the rest as GPIO. (Or bottom 16 and rest as GPIO).
There are only a number of combinations allowed.

> What are the limiting values of the voltage on the pins when the 3.3V
> for the external rail is not present(The 1.8V for the core will be on
> all the time)?

Sorry - cannot help you with this.

Regards
Anton Erasmus --
A J Erasmus



Thank you very much!
I was not shure about the address lines A23-A2, now I am OK.
About the second question - yes, I figure it out.
--- In , "Kerem Or" <k.or@s...> wrote:
> 1) You can use external memory interface pins as GPIO.
> 2) You can check max input current of a pin under "absolute
maximum ratings"
> in the datasheet. Use a series resistor to limit the input
current. The
> resistor should be low enough not to degrade switching
characteristics
> because of the I/O capacitances/inductances and high enough to
limit the
> input current when 5V or whatever the voltage is applied to the
input.
> Usually the max input current is between 5-10 mA. For instance, a
2K series
> resistor would limit the input current to 2.5mA when 5V is
applied. Assuming
> this is protect the input from a transient condition, you should
be fine.
> But if the switching speed is high then 2K resistor will
drastically affect
> rise and fall times and will add propagation delay.
> It is totaly up to your application. But the idea is it is not the
voltage
> that destroys the input but the current.
>
> Kerem >
>
> ----- Original Message -----
> From: "Zdravko" <bodhisatva@m...>
> To: <>
> Sent: Tuesday, December 21, 2004 11:41 AM
> Subject: [lpc2000] LPC2214 questions > >
> >
> > Hello,
> > I am going to use LPC2214.
> > I have some questions which are not clear for me in the User
Manual.
> >
> >
> > 1) Can I use the not used external memory bus address lines as
GPIO
> > (A0 and A1 are directly mentioned in the UM but the others not)?
> > 3) What are the limiting values of the voltage on the pins when
the
> > 3.3V for the external rail is not present(The 1.8V for the core
will
> > be on all the time)?
> >
> > Thank you very much and Happy Holidays.
> >
> > Regards
> > Zdravko
> >
> >
> >
> >
> >
> >
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
> >
> >
> >