[psas-avionics] lpc2378 SPI channel selection..

Daniel Ferguson danieljayferguson at gmail.com
Sat Aug 14 20:56:53 PDT 2010

Hi All,

Thanks for all your insight.

The board in question is an Olimex LPC2378-STK dev board:

It is not the normal lpc2378 dev board used by PSAS.
The normal one would be here:

the major difference is that the STK has an LCD panel. I have this
particular board because i accidentally deviated.

Ok so,

The SPI pins without the number suffix belong to the SPI block itself.
The SPI pins with the number suffix belong to the SSP block.

I would like to use the SPI block, and not the SSP block.
the LCD is on the SSP block.


Looking closely at the stk schematics,

You'll notice that,
SPI pin, MOSI(P0.18), is seemingly unexposed to the outside world.
So from my fresh-faced perspective, SPI is unusable on this board as-is.

In case I truly cannot use SPI(sans SSP), I need a backup plan...
SSP0 goes to the LCD. And, it's not exposed via headers as-is. so SSP0 is

That leaves me with SSP1
So, SSP1 will do, but it doesn't let me use the interrupts that the SPI/SSP0
give me.

So, now i'm looking for a confirmation that what i said isn't too far off.


On Sat, Aug 14, 2010 at 7:24 PM, David H. Madden <dhm at mersenne.com> wrote:

> On 08/14/2010 06:16 PM, Jeremy Booth wrote:
>> If I'm reading that right, the chip select for the LCD is SSEL0
>> (P1.21/PWM1.3/SSEL0 - pin 50) and if you de-assert that, the LCD should no
>> longer respond to the SPI bus.  You should be able to add several things
>> to
>> SPI0 if you are so inclined, and assert their chip selects as appropriate.
> I think that's right.  On the LPCs, you can set each pin's function
> individually.  So even though P50 can be connected to SSEL0, you don't have
> to hook it up there (through the Pin Connect Block).  You could leave it as
> P1.21, and when you want to SPI to the LCD, just wiggle P1.21 before you
> send bytes to the SPI peripheral.  If you want to talk to something else,
> leave P1.21 high and take a different GPIO, which you've connected to ~CS on
> that something else, and make it low.
>  The header pin configuration looks odd though.  Maybe it's not pinned out
>> for SPI0?
> Dunno, I don't know what board you're using (Olimex development board or
> PSAS special?)  I'm looking forward to seeing it next Tuesday...
> --
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> - Small Business, Startup and Intellectual Property Law -
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