[psas-avionics] lpc2378 SPI channel selection..

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


Hi All,

First,
Thanks for all your insight.

David,
The board in question is an Olimex LPC2378-STK dev board:
http://www.olimex.com/dev/lpc-2378stk.html

It is not the normal lpc2378 dev board used by PSAS.
The normal one would be here:
http://www.olimex.com/dev/lpc-p2378.html

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.

Unfortunately:

Looking closely at the stk schematics,
http://www.olimex.com/dev/pdf/ARM/LPC/LPC2378-STK-revC-sch.pdf

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
out.

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.

Cheers,
DanielF









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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