Hi John,

Thanks for your interesting answer:

Have you already try ?

Is it possible to translate this method to serial link (2 wires)

>  |So, what techniques are people using to make sure that the salve pics
>  |always detect the start bit of a host request message even tho they
>  |might be in the middle of doing something ??
>
>  One handy trick (for some applications) is to have the slaves always
>  listening for incoming data except when a command is sent which says,
>  in essense, "now go do stuff".  Once that command is sent, the master
>  must then refrain from sending data over the bus or else it might not
>  be heard.  The "now go do stuff" may be implicit in some or all comm-
>  ands, or it may be explicit (e.g. if your PICs are controlling stepper
>  motors, you could have commands to load each PIC's intended position,
>  and then a command to make them all go "there").
>
>  Another trick, if each command/packet is preceeded by a null or break
>  in addition to some other form of block header is to have the slave
>  units check  the state of the communications line in their main loop.
>  If it's high, the master isn't in the process of sending a null or
>  break.  The slaves then only need to check the line fast enough to
>  ensure that they don't miss the entire null or break; they may get a
>  fair number of false triggers (since the line will sometimes be low
>  because the master's sending other data) but as soon as the slave finds
>  out it false-triggered it can resume its main loop.
>
>  Both of these tricks can be very useful if the slave units have to perform
>  tasks like RC pot measurement which are time critical while they're being
>  done, but which do not need to be done at absolutely regular intervals.  In
>  some cases, of course, other methods will be more suitable.
>