SPI interface

[[email protected]]

Hi, I'm a newbie so excuse the dumb question. Trying to implement an
SPI interface between one master and multiple slaves. One of the slaves
is on an external board and i've only got 3 pins available for
connection to Master board(Its a PCB and i'm adding this slave). Now,
the SPI interface requires 4-wires(I need the Slave Select) if the
slave is "transmit only" can i leave the SDI pin unconnected (Datasheet
doesn't say much)??

P.Sevices are pics.

Thanks

 

[martin.shoebridge]

You could do it with some special software....... Assume devices 1,2 and 3
are served by SlaveSelect. The 4th device can "listen" to all commands over
SPI and you can give it a software address of 4 so it will only respond to
its own address.

 

[Spehro Pefhany]

Hi, I'm a newbie so excuse the dumb question. Trying to implement an
SPI interface between one master and multiple slaves. One of the slaves
is on an external board and i've only got 3 pins available for
connection to Master board(Its a PCB and i'm adding this slave). Now,
the SPI interface requires 4-wires(I need the Slave Select) if the
slave is "transmit only" can i leave the SDI pin unconnected (Datasheet
doesn't say much)??

You can tie it to Vdd or Vss, preferably through a resistor.

P.Sevices are pics.

Thanks

My condolences. Be sure to study all the errata documentation
carefully.


Best regards,
Spehro Pefhany

 

[Rich Grise]

Hi, I'm a newbie so excuse the dumb question. Trying to implement an SPI
interface between one master and multiple slaves. One of the slaves is on
an external board and i've only got 3 pins available for connection to
Master board(Its a PCB and i'm adding this slave). Now, the SPI interface
requires 4-wires(I need the Slave Select) if the slave is "transmit only"
can i leave the SDI pin unconnected (Datasheet doesn't say much)??

I would think not, because if your "transmit only" is sending all of the
time, it would step on the transmissions from all of your other slaves,
unless you've worked out some kind of protocol to get around that. And
if it's not free-running, how do you tell it when to send?

P.Sevices are pics.

And, along with Spehro, I send my condolences. ;-)

Good Luck!
Rich

 

[colin]

Hi, I'm a newbie so excuse the dumb question. Trying to implement an
SPI interface between one master and multiple slaves. One of the slaves
is on an external board and i've only got 3 pins available for
connection to Master board(Its a PCB and i'm adding this slave). Now,
the SPI interface requires 4-wires(I need the Slave Select) if the
slave is "transmit only" can i leave the SDI pin unconnected (Datasheet
doesn't say much)??

P.Sevices are pics.

if they are all pics you can probably use the SPI pins as general IO anyway
and devise your own interface.

I recently knocked together a circuit to program a SPI PLL device from just
1 wire conected to a rs232
(well and ground as well of course)
using 3 cmos schmitt triggers wired as delays and 'diode or' diferent length
pulses would generate data, clock and latch.

writing ~,p,@ would generate 0,1,latch.

colin =^.^=