Underclocking ARM and SRAM

I have an LPC3180 header board that needs 10MHz+ crystals to run per
spec. I plugged in a ~2MHz crystal and it ran, as slow as expected.

I've underclocked PIC parts down to being static, even using a button
as a clock. Can this be done with ARM MCUs? Can this be done with ARM
MCUs interfaced with SRAM chips?

On 11 Aug 2006 13:23:01 -0700, "ghazanhaider" <ghazan.haider@gmail.com> wrote:

>I have an LPC3180 header board that needs 10MHz+ crystals to run per
>spec. I plugged in a ~2MHz crystal and it ran, as slow as expected.
>
>I've underclocked PIC parts down to being static, even using a button
>as a clock. Can this be done with ARM MCUs? Can this be done with ARM
>MCUs interfaced with SRAM chips?

Read the datasheet - there should be a min clock freq spec - if this is 0 Hz, it will work!
SRAM certainly won't have a problem.

In article <us1qd21qhijfiphc5ed1u362j9ibrqv7e3@4ax.com>, 
mike@whitewing.co.uk says...
> On 11 Aug 2006 13:23:01 -0700, "ghazanhaider" <ghazan.haider@gmail.com> wrote:
> 
> >I have an LPC3180 header board that needs 10MHz+ crystals to run per
> >spec. I plugged in a ~2MHz crystal and it ran, as slow as expected.
> >
> >I've underclocked PIC parts down to being static, even using a button
> >as a clock. Can this be done with ARM MCUs? Can this be done with ARM
> >MCUs interfaced with SRAM chips?
> 
> Read the datasheet - there should be a min clock freq spec - if this is 0 Hz, it will work!
> SRAM certainly won't have a problem.

For an external crystal, the LPC3180 accepts from 1 to 20 MHz.
It also has an internal 32.768KHz oscillator, which can drive the system 
clock at 13 MHz via a PLL.

--Gene

Gene S. Berkowitz wrote:
> In article <us1qd21qhijfiphc5ed1u362j9ibrqv7e3@4ax.com>,
> mike@whitewing.co.uk says...
> > On 11 Aug 2006 13:23:01 -0700, "ghazanhaider" <ghazan.haider@gmail.com> wrote:
> >
> > >I have an LPC3180 header board that needs 10MHz+ crystals to run per
> > >spec. I plugged in a ~2MHz crystal and it ran, as slow as expected.
> > >
> > >I've underclocked PIC parts down to being static, even using a button
> > >as a clock. Can this be done with ARM MCUs? Can this be done with ARM
> > >MCUs interfaced with SRAM chips?
> >
> > Read the datasheet - there should be a min clock freq spec - if this is 0 Hz, it will work!
> > SRAM certainly won't have a problem.
>
> For an external crystal, the LPC3180 accepts from 1 to 20 MHz.
> It also has an internal 32.768KHz oscillator, which can drive the system
> clock at 13 MHz via a PLL.
>
> --Gene

Oops! I meant an LPC2138. Its minimum per user manual and datasheet is
10MHz.

I've been keeping an eye on the lpc3180 and its been on my mind.
Samples arent out yet.

ghazanhaider wrote:
> Gene S. Berkowitz wrote:
> > In article <us1qd21qhijfiphc5ed1u362j9ibrqv7e3@4ax.com>,
> > mike@whitewing.co.uk says...

> > For an external crystal, the LPC3180 accepts from 1 to 20 MHz.
> > It also has an internal 32.768KHz oscillator, which can drive the system
> > clock at 13 MHz via a PLL.
> >
> > --Gene
>
> Oops! I meant an LPC2138. Its minimum per user manual and datasheet is
> 10MHz.

Interesting.  I wonder why it's minimum is higher than other members of
the family (such as the 2106)?

Robert

>
> Interesting.  I wonder why it's minimum is higher than other members of
> the family (such as the 2106)?
>
> Robert

I dont know but I intend to play with much lower frequencies. Maybe its
for the DAC and UARTs, I wont need em. Maybe ISP wont work. But last I
tried a blinky prog 2MHz worked great. Crystal I mean.

ghazanhaider wrote:
> >
> > Interesting.  I wonder why it's minimum is higher than other members of
> > the family (such as the 2106)?
> >
> > Robert
>
> I dont know but I intend to play with much lower frequencies. Maybe its
> for the DAC and UARTs, I wont need em. Maybe ISP wont work. But last I
> tried a blinky prog 2MHz worked great. Crystal I mean.

As I recall, on the other members, the UARTs worked fine (not
surprising) but ISP expected 10MHz or better.  The big issue was the
PLL which required a minimum of 10MHz input.

Maybe the ADC has some timing limitations (Maybe hold time on the S/H?)
but I would have thought the DAC to be all right. 

Robert

sub2@aeolusdevelopment.com wrote:

> As I recall, on the other members, the UARTs worked fine (not
> surprising) but ISP expected 10MHz or better.  The big issue was the
> PLL which required a minimum of 10MHz input.
>
> Maybe the ADC has some timing limitations (Maybe hold time on the S/H?)
> but I would have thought the DAC to be all right.
>
> Robert

Well, I'm aiming for a really low power system, and will start testing
underclocking the lpc2138 first. The pll divider only takes me to about
1MHz or a little less... but if the 2MHz crystal test worked so should
possibly a 32KHz. In the longer run I have the lpc2888 in mind, but
thats a bigger testing rig at 1.8V plus the low power sram and flash.
That thing has a 10MHz limit too and its timing with sram and flash
will be tricky. Gotta make it work.

Gotta be the first one to make a solar powered linux computer that you
can put in your pocket!

Currently I need a square foot of panel in a bright indoor room as a
minimum. Aint got pockets that big.

ghazanhaider wrote:
> sub2@aeolusdevelopment.com wrote:
>
> > As I recall, on the other members, the UARTs worked fine (not
> > surprising) but ISP expected 10MHz or better.  The big issue was the
> > PLL which required a minimum of 10MHz input.
> >
> > Maybe the ADC has some timing limitations (Maybe hold time on the S/H?)
> > but I would have thought the DAC to be all right.
> >
> > Robert
>
> Well, I'm aiming for a really low power system, and will start testing
> underclocking the lpc2138 first. The pll divider only takes me to about
> 1MHz or a little less..

The datasheet has power consumption numbers down to 0 Hz (on the
graph), maybe there is another clock divide down somewhere like on the
Atmel ARM's.

OK heres an update.

A 2MHz and a 1.8432MHz rectangular crystal both worked, but a
cylindrical 32.76kHz crystal failed. With the 2MHz and PLL divider at
16 it will run at 125kHz.

I think I'll go xtal shopping till I find the slowest and lowest power
at which it'll work, then I'll do it with the lpc 2888 or lpc3180
(whichever is at 1.8V) for the lowest power.