Lpc2000

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

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@...>
To: <lpc2000@yahoogroups.com>
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 lpc2000@yahoogroups.com, "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: <lpc2000@yahoogroups.com>
> 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
> >
> >
> >
> >
> >
> >
> >
> >