Master and slaves

Master and slaves

Introduction -- Master and Slaves

Slaves

Dallas/Maxim makes a series of chips called 1-wire slaves.

  • Each has a unique ID number (8 bytes)

    • The first byte is the Family code and gives the type of chip

    • The next 6 bytes are a unique ID number

    • The last byte is a check byte

  • All the slaves can be connected on a common wire (well, you need a ground wire too).

    • Data is sent along this wire.

    • The slaves steal power from the comminucation (parasytic power)

    • The slaves can announce their presence and ID

    • The slaves can be individually addressed.

Some slaves

1-wire slaves on parade

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:

Multitemp

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).

  • The type of wire isn't too important. It carries 5V and little current.

  • A single line is far preferable to a branching pattern.

  • With care, the total length can extend to a few hunder meters.

    • OWFS makes long runs less common

    • It is easy to partition the network.

    • Wireless (wifi) hubs.

Chained slaves

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

Master and slaves

Finally, the full picture.

The slaves signal by allowing the voltage to be high, or shorting it to ground.

  • The bus master sets and reads the line voltage

  •  The bus master initiates all communication

  •  The bus master connects to the computer via

    •  USB

    •  serial port

    •  network

    •  direct

    •  parallel port

    •  i2c