will also need to know when the point has been changed, and would
probably also like to know when it can ask to change another.
+The currently envisaged PCBs can support up to 104 point motors.
+
BLOCK SENSE
===========
Changing takes 1-10ms.
+The currently envisaged PCBs can support up to 18 reversible segments.
+
+
*** PROVISIONAL: ***
It may prove necessary to temporarily disable track power during
certain polarity changes.