Lpc2000

Hello,
I just would like to know if a lithium cell connect to Vbat on a LPC2138 save only the RTC or if it also save the SRAM contents ?

Thanks,
Sebastien

[Non-text portions of this message have been removed]

The Vbat is strictly for the RTC.  In low power power-down mode the 
SRAM contents are preserved, but around 60uA of power is drawn from 
Vdd.  I suppose it would be possible to have your lithium battery with 
latch to a transistor to Vdd.  That way you could dynamically set the 
latch to enable power from Vbat to Vdd, then place the processor into 
low-power shutdown mode, and when you resume clear the latch to remove 
the battery from the circuit.  Depending on your battery voltage a 
simple diode may also work, but you'll need to be careful in how you 
handle that to ensure that you don't try to remain on via lithium 
battery voltage.  If you wanted to do something like this then having 
a removable coin-cell lithium is probably your best bet so that you 
can replace it when it runs out :)


--- In lpc2000@yahoogroups.com, "Sebastien Jacquemard" 
<sejacquemard@w...> wrote:
>
> Hello,
> I just would like to know if a lithium cell connect to Vbat on a 
LPC2138 save only the RTC or if it also save the SRAM contents ?

> 
> Thanks,
> Sebastien
> 
> [Non-text portions of this message have been removed]
>

Thank you.

Sebastien
----- Original Message ----- 

From: "seangra" <sgraham@...>
To: <lpc2000@yahoogroups.com>
Sent: Thursday, November 24, 2005 8:37 PM
Subject: [lpc2000] Re: Vbat on LPC2138


> The Vbat is strictly for the RTC.  In low power power-down mode the 
> SRAM contents are preserved, but around 60uA of power is drawn from 
> Vdd.  I suppose it would be possible to have your lithium battery with 
> latch to a transistor to Vdd.  That way you could dynamically set the 
> latch to enable power from Vbat to Vdd, then place the processor into 
> low-power shutdown mode, and when you resume clear the latch to remove 
> the battery from the circuit.  Depending on your battery voltage a 
> simple diode may also work, but you'll need to be careful in how you 
> handle that to ensure that you don't try to remain on via lithium 
> battery voltage.  If you wanted to do something like this then having 
> a removable coin-cell lithium is probably your best bet so that you 
> can replace it when it runs out :)
> 
> 
> --- In lpc2000@yahoogroups.com, "Sebastien Jacquemard" 
> <sejacquemard@w...> wrote:
> >
> > Hello,
> > I just would like to know if a lithium cell connect to Vbat on a 
> LPC2138 save only the RTC or if it also save the SRAM contents ?
> > 
> > Thanks,
> > Sebastien
> > 
> > [Non-text portions of this message have been removed]
> >
> 
> 
> 
> 
> 
> 
> 
>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 
>

--- In lpc2000@yahoogroups.com, "Sebastien Jacquemard" 
<sejacquemard@w...> wrote:
>
> Hello,
> I just would like to know if a lithium cell connect to Vbat on a 
LPC2138 save only the RTC or if it also save the SRAM contents ?
> 
> Thanks,
> Sebastien
> 
> [Non-text portions of this message have been removed]
>

Vbat on the LPC2138 and LPC2148 keeps only the RTC alive. To keep the 
SRAM up, you need to go into power down mode with a voltage connected 
to Vdd.
On the new LPC2101/2/3, Vbat can also buffer the SRAM.

Regards, Robert