Master and slaves
Introduction -- Master and Slaves
Slaves
Dallas/Maxim makes a series of chips called 1-wire slaves.
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Each has a unique ID number (8 bytes)
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The first byte is the Family code and gives the type of chip
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The next 6 bytes are a unique ID number
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The last byte is a check byte
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All the slaves can be connected on a common wire (well, you need a ground wire too).
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Data is sent along this wire.
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The slaves steal power from the comminucation (parasytic power)
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The slaves can announce their presence and ID
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The slaves can be individually addressed.
Some slaves
Notice that each slave has a unique number. The type is also shown.
No two slaves are alike
More than one slave of the same type can be included:
Here there is more than one temperature chip. With the unique ID, they can be distinguished.
Chain gang
But the slaves need to be connected. A single line (plus ground).
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The type of wire isn't too important. It carries 5V and little current.
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A single line is far preferable to a branching pattern.
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With care, the total length can extend to a few hunder meters.
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OWFS makes long runs less common
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It is easy to partition the network.
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Wireless (wifi) hubs.
We are still missing something.
All these chips are passive (that's why they are called slaves).
They don't initiate a signal.
They can't talk to each other.
Master and slaves
Finally, the full picture.
The slaves signal by allowing the voltage to be high, or shorting it to ground.
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The bus master sets and reads the line voltage
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The bus master initiates all communication
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The bus master connects to the computer via
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USB
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serial port
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network
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direct
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parallel port
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i2c
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