[Oberon] PO2013 - Real time measurement

[Paul Reed]

> How about extending board's SPI socket, into a sort of cable bus,
> devices put on a ribbon cable. Then question remains, how to address the
> nodes using distinct CS signal for each, also not sure what length of
> ribbon cable could SPI handle. It is meant just for sensor logic in
> immediate vicinity of FPGA board. The analog signals will be carried by
> longer cables to actual sensors / probes.

It's wise not to be too general about this but just design for some
specific examples.  I2C attempts to solve the multiple-select-line problem
by having devices respond to a (sometimes-configurable) address instead,
but I2C is much more complicated than SPI (in implementation more than in
use).

Long analogue lines are usually avoided, because of the possibility of
interference and attenuation.  Hence I suggested radio as being much
easier nowadays; but you could use e.g. RS485.  Tradeoffs for distance vs
baudrate are usually made; in the case of sensors this is not usually a
problem.

HTH
Paul