User manual

UDOO Starting manual (beta) Version 0.4
http://www.udoo.org/
30"
A. GPIOs can be used to build a communication channel between the two
processors. By setting one processor in INPUT mode, and the other in OUTPUT
mode, a one-way channel will be created. Via software, it is possible to switch
the direction on both processors, in order to create a half-duplex
communication channel.
B. Two processors simultaneously can read data from external devices. They can
also write data to external devices or the other processor, but only one at a
time can be set in output mode.
C. The situations here illustrated must be avoided. In the first case, both
processors set the shared pin in output mode. If they try to drive the shared
line with different signal values, the resulting signal level will be unpredictable
and it could result in damaging the processor driving the signal LOW. The
same situation occurs when one external device tries to drive the shared line.
WARNING!
There isn’ t any automatic tool that can avoid dangerous situations. The programmer
must develop Hardware and Software able to avoid the occurrence of dangerous
situation.