On Wed, Oct 20, 2004 at 06:49:33PM -0400, Dan McMahill wrote: > On Wed, Oct 20, 2004 at 09:41:40AM -0400, Randall Nortman wrote: [...] > > 2) I would like to be able to extend the SPI and I2C buses between > > stacked boards for short distances (perhaps three boards stacked > > 1.5" apart with about 4" total cable length). I'm thinking that > > flat ribbon cable with every other conductor attached to ground > > should provide enough crosstalk dampening for such short distances. > > Does this seem reasonable, or am I going to have reflection > > problems? (The boards themselves will have traces up to about 5" > > long carrying these signals, which also needs to be considered.) > > I'd just put 100 ohms or so in series with the drivers. At the speeds > you're running at for the SPI and I2C, you can afford to slow down the > edges enough to make your cable more or less look like a lumped circuit.
There are several drivers on each bus (other than the SPI master-out line, which has one driver and multiple receivers). I2C is bi-directional, and SPI puts multiple slaves on the same line. Do you advise a resistor in front of each driver? I assume you advise this in addition to the pull-up resistors on the I2C lines, right? Thanks, Randall
