Hi Rajendra (Mark),
Mark has covered SPI operation very well, that's the nuts and bolts of it.
Maybe one last remark to make it sink in a bit easier again.
Think of SPI as a 16 bit shift register, with a "Master" as 8 bit shift register,
and a Slave as an 8 bit shift register, and with a feedback from the output of bit 15
into bit 0.
Thus, all that happens is that Master and Slave _exchange_ their 8 bits when the
8 clock pulses are issued. No matter which side (ie. Master or Slave), data is read
on one edge of clock pulses, while data is output on the opposite edge of the clock pulse.
This means the Master for example can change the "1" or "0" data output while it's
reading the data line, since the Slave is NOT sampling MOSI at that moment, and vice-versa
for the Slave with MISO.
The only thing that qualifies a Master from a Slave is whom issues the clock pulses.
Hence the whole system is synchronous.
There might even be times where it is handy to "hold" the SPI transfer. That even can
be one in HW : Some SPI (SLAVE) devices have a /HOLD input pin.
(A bit restricting IMO, because you can only change /Hold when clock "idle").
Because you can clock data at rising or falling edge - and - you can keep your clock "Idle"
High or Low _between_ bit transfers, there are FOUR combinations ::::
referred to sometimes as SPI Mode 0,1,2 and 3.
Happy trails
-- Kris
> Hallo Rajendra
>
> When the SPI (master) sends 8 bits of data over the MOSI line it
> also clocks in 8 bits of data via the MISO line. Therefore when a
> byte of data has successfully been sent (SPI_SPSR & 0x80 becomes
> true) it also has a byte of received data which can be read from
> SPI_SPDR. (when no slave it is probably 0xff or 0x00 depending on
> the line state - if the slave has nothing to send it depends on the
> device - eg. the LPC210x in slave mode sends byte the last received
> byte)
>
> This means that the slave must prepare and send data - the exact
> sequence will depend on your peripheral device but it generally
> means that you must first send a command byte to inform which data
> it should sent to you and then you can read it (one or a sequence of
> bytes). If the master has no data to send while reading the byte(s)
> it can send a dummy byte (0xff or 0x00 etc.).
>
> The code to send and also read in full duplex (assuming the slave
> supports it) could look like this:
>
> void fnSendReceive(unsigned char *out, unsigned char *in, unsigned
> short usLength)
> {
> while (usLength--) {
> IOCLR = SPI_SSEL_OUT; // activate SSEL
> SPDR = *out; // send data byte
> while (!(SPSR & SPIF)) {}; // wait for transmission to
> complete
> IOSET = SPI_SSEL_OUT; // remove SSEL
> *in++ = (unsigned char)SPDR; // save data
> }
> }
>
> Note that the LPC210x has a very simple SPI which has only one
> interrupt flag to indicate when the transmission has completed and
> the received data is available. There is no buffering in the
> transmitter and so it is imperative that the flag is set before
> sending the next byte otherwise it may be lost - as consequence the
> throughput tends to suffer since the software processing has to take
> place almost completely between transmission periods and it is
> hardly possible to do any work during the byte transmission interval.
>
> Regards
>
> Mark Butcher
>
> www.mjbc.ch
>
>
> --- In lpc2000@yahoogroups.com, "rockraj_2003" <rockraj_2003@y...>
> wrote:
> >
> > Hello Mark,
> >
> > Thanks for Ur Response.I tried Ur Code its working fine.
> > I aslo changed my prog.This Code is also giving the Same response.
> > I didn't CLR the SSEL pin at all.But I regularly changed SPIF to
> 0x00.
> >
> > Now, my doubt is if i want to use MISO as well what should i do.
> > Since in the Data Sheet THE mentioned SPI as duplex.
> >
> > How I can use MISO.
> >
> > Silly Question, but I don't know about this.
> > If the SPI is in MOSI, it can send DATA (MASTER OUTPUT) at the
> Same
> > time it receive data in SLAVE.(SLAVE INPUT).How much time it will
> > wait to receive DATA. If again I put some Data to the SPI_SPDR it
> > will transmit or it will wait to receive.
> >
> > > > #define SPI_SPCR (*((volatile unsigned char *)
> 0xE0020000))
> > > > #define SPI_SPSR (*((volatile unsigned char *)
> 0xE0020004))
> > > > #define SPI_SPDR (*((volatile unsigned char *)
> 0xE0020008))
> > > > #define SPI_SPCCR (*((volatile unsigned char *)
> 0xE002000C))
> > > > #define SPI_SPTCR (*((volatile unsigned char *)
> 0xE0020010))
> > > > #define SPI_SPTSR (*((volatile unsigned char *)
> 0xE0020014))
> > > > #define SPI_SPTOR (*((volatile unsigned char *)
> 0xE0020018))
> > > > #define SPI_SPINT (*((volatile unsigned char *)
> 0xE002001C))
> > > >
> > > > int main (void)
> > > > {
> > > > int i;
> > > > VPBDIV = 1;
> > > > IODIR = 0x80;
> > > > IOSET = 0x80;
> > > > PINSEL0 = 0x5500;
> > > > SPI_SPCCR = 0x93;
> > > > SPI_SPCR = 0x20;
> > > > while (1) {
> > > > do SPI_SPDR = 0x55;
> > > > while((SPI_SPSR & 0x80)==0);
> > > > SPI_SPSR = 0x00;
> > > > do SPI_SPDR = 0x0F;
> > > > while((SPI_SPSR & 0x80)==0);
> > > > SPI_SPSR = 0x00;
> > > > do SPI_SPDR = 0xF0;
> > > > while((SPI_SPSR & 0x80)==0);
> > > > SPI_SPSR = 0x00;
> > > > }
> > > > }
> >
> >
> > with Regards
> > Rajendra R
> >
>
>
>
>
>
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