Multiple SPI ports, absurd? Well, no.

Started by Bruce McMillan October 10, 2003
User feedback.
The SPI port is designed to multiplex many peripherals in a polling
fashion. So why would you want more than one?

Well, I have found it useful in the past where I have needed to have
the SPI bus go into sensitive parts of the board, to say control
digital potentiometers, where to minimise noise its desireable to have
separate high speed & low speed busses.

And just now I find myself attempting to interface with an RF chip
purporting to have a 3-wire interface, but it's only when you delve
into the timing diagrams does it become apparent that this chip
assumes it has exclusive use of the 3-wire interface (chip select
doesn't tristate clock & data lines). Boy, I sure would like a second
SPI port right now.

bruce.



--- In , "Bruce McMillan"
<bruce_at_pocket_neurobics@y...> wrote:
> User feedback.
> The SPI port is designed to multiplex many peripherals in a polling
> fashion. So why would you want more than one?
>
> Well, I have found it useful in the past where I have needed to have
> the SPI bus go into sensitive parts of the board, to say control
> digital potentiometers, where to minimise noise its desireable to have
> separate high speed & low speed busses.
>
> And just now I find myself attempting to interface with an RF chip
> purporting to have a 3-wire interface, but it's only when you delve
> into the timing diagrams does it become apparent that this chip
> assumes it has exclusive use of the 3-wire interface (chip select
> doesn't tristate clock & data lines). Boy, I sure would like a second
> SPI port right now.
>
> bruce.

I know what you mean. What's worse is I have had to deal with things
that have 14 bit word lengths (and so, more bit banging).

Having a few lines driven out of an on-chip fpga-like block would be
handy. Not likely useful for 95% of applications, but still would be
pleasant.

-z


hi:

you could use a tri-state gate like an hc125 and have the slave select line
control the output enables. a little messy but it works.

regards.

ed

----- Original Message -----
From: "Mysterious Mister Z" <>
To: <>
Sent: Saturday, October 11, 2003 12:08 PM
Subject: [68HC12] Re: Multiple SPI ports, absurd? Well, no. > --- In , "Bruce McMillan"
> <bruce_at_pocket_neurobics@y...> wrote:
> > User feedback.
> > The SPI port is designed to multiplex many peripherals in a polling
> > fashion. So why would you want more than one?
> >
> > Well, I have found it useful in the past where I have needed to have
> > the SPI bus go into sensitive parts of the board, to say control
> > digital potentiometers, where to minimise noise its desireable to have
> > separate high speed & low speed busses.
> >
> > And just now I find myself attempting to interface with an RF chip
> > purporting to have a 3-wire interface, but it's only when you delve
> > into the timing diagrams does it become apparent that this chip
> > assumes it has exclusive use of the 3-wire interface (chip select
> > doesn't tristate clock & data lines). Boy, I sure would like a second
> > SPI port right now.
> >
> > bruce.
>
> I know what you mean. What's worse is I have had to deal with things
> that have 14 bit word lengths (and so, more bit banging).
>
> Having a few lines driven out of an on-chip fpga-like block would be
> handy. Not likely useful for 95% of applications, but still would be
> pleasant.
>
> -z >
>
> -------------------- >
> ">http://docs.yahoo.com/info/terms/ >