Pycom FiPy, Руководство пользователя, Страница: 175 / 496

break
return devices
def _search_rom (self, l_rom, diff) :
if not self.reset():
return None , 0
self.write_byte(CMD_SEARCHROM)
if not l_rom:
l_rom = bytearray( 8 )
rom = bytearray( 8 )
next_diff = 0
i = 64
for byte in range( 8 ):
r_b = 0
for bit in range( 8 ):
b = self.read_bit()
if self.read_bit():
if b: # there are no devices or there is an error on the bus
return None , 0
else :
if not b: # collision, two devices with different bit meaning
if diff > i or ((l_rom[byte] & ( 1 << bit)) and diff != i):
b = 1
next_diff = i
self.write_bit(b)
if b:
r_b |= 1 << bit
i -= 1
rom[byte] = r_b
return rom, next_diff
class DS18X20 (object) :
def __init__ (self, onewire) :
self.ow = onewire
self.roms = [rom for rom in self.ow.scan() if rom[ 0 ] == 0x10 or rom[ 0 ] == 0x28
]
def isbusy (self) :
"""
Checks wether one of the DS18x20 devices on the bus is busy
performing a temperature conversion
"""
return not self.ow.read_bit()
def start_conversion (self, rom=None) :
"""
Start the temp conversion on one DS18x20 device.
Pass the 8-byte bytes object with the ROM of the specific device you want to r
ead.
If only one DS18x20 device is attached to the bus you may omit the rom paramet
er.
"""
rom = rom or self.roms[ 0 ]
4.2.9 Onewire Driver
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