I think in this current context we are talking about distances of not much more than 10 centimeters. The signal would go from a GPOI header to a real-time controller like an FPGA or uP. In typical use cases, SPI and I2C never leave the PCB and don't go over cables, although it could especially in one-off prototype work
On Wed, Mar 27, 2019 at 11:42 AM Rafael Skodlar <[email protected]> wrote: > We are making progress... > > On 3/27/19 11:16 AM, Chris Albertson wrote: > > What makes SPI nice is not it's speed. On the Pi it can go up to 250 > MHz, > > so Ethernet beats it for speed and Ethernet cables can be 100 meters > long. > > SPI wins because it is fast enough for most things and is very simple, > > just connect the wires. But it only works over a short distance. But > it > > is SIMPLE, conceptually no unlike TTL level serial. > > Let's see what one of my former employers, an IC manufacturer has to say > about SPI: > https://www.maximintegrated.com/en/app-notes/index.mvp/id/6208 > "The maximum distance of an I2C bus depends on the capacitive loading. > In typical applications, the length is limited to a few meters in > standard mode. This is because a system has to be built to accommodate a > maximum bus capacitance of 400pF to meet rise time requirements listed > in the I2C bus specification (Rev. 6 – 4 April 2014)." > > Still want to use parallel port? ;-) > > > > > Ethernet needs some support hardware, a small transformer at least. > > Not necessarily. There is plenty of boxes connected with fiber cable. > Seen that done that. > > > > > Unlike simply using GPIO pins, SPI does not need much CPU time to send > data. > > > > But if writing software you should not have to decide of lock in a > certain > > communications method. I like whatht ehauthors is ros-serial did, that > > w=said "Use any communications method that has these four fuctions: open, > > close, read, write. THat pretty much means anything from a network > socket > > to an RS232 cable. > > > > All protocols have some kind of handshake. If designed properly then > dedicated circuits to handle interrupts take care of it. That beats > anything that I've seen years ago in one over 40 years old CNC machine > where transistors and other discrete components were in such odd shape I > wasn't sure what they were in most cases. > > You could extend SPI connection with optical drivers and fiber optic > cables also. 1km distance would not be impossible. Granted, this would > be theoretical more than a practical solution not sensitive to electric > noise or atmospheric electric discharge that killed a lot of RS-232 > circuits which I ended up replacing with 60mA loops in my career. > > -- > Rafael Skodlar > > > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
