Lpc2000

That is usually the case. In order to read a byte from a slave register you
must transmit a "dummy" byte from the master. By putting 0x00 in the SPI
data register you will initiate the SPI cycle. Once the dummy byte has been
shifted out your SPI data register will hold the value from the slave.

Master controls the SPI transfer.. every time you send something from the
master by putting something in the data register you will get back something
from the slave. Sometimes that might be garbage that you disregard, and at
other times it is what you need. I assume that in your case you have to send
the control byte to start the AD conversion and then your result is waiting
for you in the register of the slave. 

If you change the MOSI to GPIO the SPI module will not generate the clock
signal, hence your AD converter is not going to shift anything out.

Hope this helps.

Cheers,

m.

PS: don't forget the famous SSEL that has to be pulled high if LPC210x is
your only master on the bus, by means of pull up resistor or by tying it to
VDD.

 

  _____  

From: Rodrigo [mailto:rodrigo@...] 
Sent: Monday, June 07, 2004 8:57 AM
To: lpc2000@yahoogroups.com
Subject: [lpc2000] SPI

 

I'm trying to communicate with a AD converter through a SPI interface. In
the AD datasheet, it's said that I need to have DIN line (from AD) in low
level when it's transmitting. This means that I have to write 0x00 on MOSI
line while i'm receiving the data. The problem is, there's just one data
register, can I do that? If I can't, can I change just the MOSI pin to GPIO
mode and put on low level while I'm receiving data?

 

Rodrigo Martins

Dpto. Projeto

Intermetric Instrumentos Ltda

 






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