This will put the LANC line low which is seen by
the camcorder (refer to Figure 8 blue lines).
After sending a command byte, we clear the
loss-of-signal timer and flag. When both bytes
have been transmitted, we drop into a loop that
will receive the next six bytes of the stream and
move them to the hub buffer (see full listing).
That's the hard work of the PASM code.
There is one small bit that is used in special
cases. If the camcorder is put into or goes into
power-down/sleep mode, we can wake it by
pulling the LANC line low for at least 140
milliseconds. This is not a serial signal; it's a
brute force thing. Many LANC devices
(including my first controller) have a normally-open pushbutton between the LANC line and
ground; this button is used to wake a sleeping
camera. The interface we're using allows us to
do this with software. The wake command puts
■ FIGURE 9. LANC control demo.