A previous version of the 1-wire driver (which was recently replaced by the
current one) had this behaviour and it allows to create a 1-wire bus
without any external pull-up resistors.
These drivers can now be used by any port (so long as that port has the
_onewire driver from extmod/modonewire.c).
These drivers replace the existing 1-wire and DS18X20 drivers in the
drivers/onewire directory. The existing ones were pyboard-specific and
not very efficient nor minimal (although the 1-wire driver was written in
pure Python it only worked at large enough CPU frequency).
This commit brings backwards incompatible API changes to the existing
1-wire drivers. User code should be converted to use the new drivers, or
check out the old version of the code and keep a local copy (it should
continue to work unchanged).
The driver seems to be be enabling the pullup resistor in most places, but
not this one. Making this one little change allows onewire devices to be
used with no external pullup resistor.
