Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > sci.electronics.design > #454028

Re: Output boards, SPI vs I2C

Show all headers | View raw

On 2017-03-28, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
> On 03/27/2017 07:07 PM, Martin Riddle wrote:
>> On 27 Mar 2017 18:41:59 GMT, Jasen Betts <jasen@xnet.co.nz> wrote:
>> 
>>> On 2017-03-27, rickman <gnuarm@gmail.com> wrote:
>>>> On 3/26/2017 3:49 PM, David Lesher wrote:
>>>>> rickman <gnuarm@gmail.com> writes:
>>>>>
>>>>>>> Not sure I follow; there is SPI on the board, but thinking out
>>>>>>> loud, we would have to add selection to the existing SPI users,
>>>>>>> the display, touch screen, and flash.....
>>>>>
>>>>>> Flash???  The other stuff is up to you.   I"m just talking about the 24
>>>>>> relays.  You didn't mention the other items.  Is everything going to be
>>>>>> on the 8 digital outputs?
>>>>>
>>>>> I was talking about using the existing I2C or SPI system to also
>>>>> drive the outboard relay boards. It's mentioned only in passing in the
>>>>> writeup.
>>>>
>>>> Yes, I saw that.  I don't have the various web pages open at the moment, 
>>>> but you may have trouble using the built in SPI port because each port 
>>>> will need an enable.  If you go this route you will need to use I2C.
>>>
>>> save some pins: use a 4017 for the enable.
>>>
>> 
>> 74HC138 Mux, 3 to 8
>> 
>> Cheers
>> 
>
> Using a 4017 is pretty gnarly--how do you avoid !CS glitches?  If you
> had a '595 buffered SIPO register on there, every time you hit its chip
> select, its output register gets loaded with whatever garbage is in the
> shift reg at the time.

the 4017 has an enable pin but that means using 3 outputs to drive it.

is the '138 guaranteed glitch free?

> Since that would require that each shift register be loaded with the
> correct data at nearly all times, you might as well daisy chain them and
> use one chip select.

yeah, if your interface parts support that, it seems the best way to go.

> Cheers
>
> Phil Hobbs
>


-- 
This email has not been checked by half-arsed antivirus software 

Back to sci.electronics.design | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Output boards, SPI vs I2C David Lesher <wb8foz@panix.com> - 2017-03-25 02:46 +0000
  Re: Output boards, SPI vs I2C krw@notreal.com - 2017-03-24 23:25 -0400
    Re: Output boards, SPI vs I2C David Lesher <wb8foz@panix.com> - 2017-03-26 04:13 +0000
  Re: Output boards, SPI vs I2C rickman <gnuarm@gmail.com> - 2017-03-25 14:04 -0400
    Re: Output boards, SPI vs I2C David Lesher <wb8foz@panix.com> - 2017-03-26 04:11 +0000
      Re: Output boards, SPI vs I2C rickman <gnuarm@gmail.com> - 2017-03-26 02:37 -0400
        Re: Output boards, SPI vs I2C David Lesher <wb8foz@panix.com> - 2017-03-26 14:41 +0000
          Re: Output boards, SPI vs I2C rickman <gnuarm@gmail.com> - 2017-03-26 12:47 -0400
            Re: Output boards, SPI vs I2C David Lesher <wb8foz@panix.com> - 2017-03-26 19:49 +0000
              Re: Output boards, SPI vs I2C rickman <gnuarm@gmail.com> - 2017-03-27 10:49 -0400
                Re: Output boards, SPI vs I2C Jasen Betts <jasen@xnet.co.nz> - 2017-03-27 18:41 +0000
                Re: Output boards, SPI vs I2C Martin Riddle <martin_ridd@verizon.net> - 2017-03-27 19:07 -0400
                Re: Output boards, SPI vs I2C Jasen Betts <jasen@xnet.co.nz> - 2017-03-28 08:03 +0000
                Re: Output boards, SPI vs I2C Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-03-28 10:44 -0400
                Re: Output boards, SPI vs I2C Jasen Betts <jasen@xnet.co.nz> - 2017-03-28 18:59 +0000
                Re: Output boards, SPI vs I2C Martin Riddle <martin_rid@verizon.net> - 2017-03-28 15:37 -0400
                Re: Output boards, SPI vs I2C David Lesher <wb8foz@panix.com> - 2017-04-03 17:49 +0000
                Re: Output boards, SPI vs I2C rickman <gnuarm@gmail.com> - 2017-04-03 15:18 -0400
                Re: Output boards, SPI vs I2C David Lesher <wb8foz@panix.com> - 2017-04-04 02:59 +0000
                Re: Output boards, SPI vs I2C rickman <gnuarm@gmail.com> - 2017-04-04 00:54 -0400
                Re: Output boards, SPI vs I2C David Lesher <wb8foz@panix.com> - 2017-03-28 05:08 +0000
                Re: Output boards, SPI vs I2C rickman <gnuarm@gmail.com> - 2017-03-28 02:16 -0400
  Re: Output boards, SPI vs I2C Martin Riddle <martin_ridd@verizon.net> - 2017-03-27 19:03 -0400
    Re: Output boards, SPI vs I2C David Lesher <wb8foz@panix.com> - 2017-03-28 03:28 +0000
      Re: Output boards, SPI vs I2C rickman <gnuarm@gmail.com> - 2017-03-28 00:38 -0400
        Re: Output boards, SPI vs I2C David Lesher <wb8foz@panix.com> - 2017-03-28 14:47 +0000

csiph-web