Lpc2000

--- In lpc2000@yahoogroups.com, MaxStream - Ryan Bedwell <ryanb@m...>
wrote:
> Art Sobel wrote:
> 
> > In the process of attaching some SPI peripherals to the chip I ran
> > into some strange  behaviour.  There are 4 pins to use, SPICLK, MISO,
> > MOSI and SSCS, First the SSCS pin must be configured as an SPI PIN or
> > the other parts of the SPI don't work at all, Next the SSCS signal is
> > not generated, This means that I must use another GPIO as the CS
> > signal. So now it uses 5 pins - with one more GPIO pin for every SPI
> > peripheral. 
> > 
> > Using the fastest selection of clocks the output rate is about 12,500
> > D/A samples a second (each D/A sample requires 2 bytes of data
> > output). This just about scratches the idea that the chip could
> > produce medium quality sound output. One channel just barely then if
> > you want to have analog in on the SPI too then the throughput just
> > dives. How the heck did they ever think this chip could do modems?
> 
> A couple of thoughts:
> 
>   - If the 21XX is always only going to serve as SPI master
>     (i.e. it will never be selected as a SPI slave), then
>     it makes sense to use a pullup on SSCS.
>   - Not sure I follow your throughput math.  The max PCLK
>     rate is 60 MHz (divide by 1 with a 60 MHz CCLK).  The
>     max SPI clock is PCLK / 8, or 7.5 MHz.  At 7.5 MHz
>     2 bytes should take 2.13 usec (468,750 samples/sec), no?
> 
> Ryan

You'd think that but i did put an 8 into the counter and all I got was
12,000 samples a sec. I programmed the port as master but the SSCS is
never generated.