Editing Local Interconnect Network (section)

== Slave node position detection (SNPD) or autoaddressing ==
These methods allow the detection of the position of slave nodes on the LIN bus and allow the assignment of a unique node address (NAD).<ref>
Anand Gopalan, Akeem Whitehead.
[http://www.ti.com/lit/an/slda038/slda038.pdf "Automatic Slave Node Position Detection (SNPD)"].
</ref>
* Allows similar or the same devices to be connected on the bus without end of line programming or connector pin programming.

Restrictions:
* All auto-addressing slaves must be in one line
** Standard slaves can be connected in any way

{| class="wikitable"
|-
! SNPD Method
! SNPD Method ID
! Company
|-
| Extra wire daisy chain
| 0x01
| [[NXP]] (formerly Philips)
|-
| Bus shunt method
| 0x02
| [[Elmos Semiconductor]]
|-
| Reserved
| 0x03
| TBD
|-
| Reserved
| 0x04
| TBD
|-
| Reserved
| 0xFF
| TBD
|}

=== Extra wire daisy chain (XWDC) ===
Each slave node has to provide two extra pins, one input, D<sub>1</sub>, and one output, D<sub>2</sub>.
* The first SNPD node input D1 is either set to GND or connected to the output of the master.
** The output of the first node, D<sub>2</sub>, is connected to the input, D<sub>1</sub> of the second node, and so on resulting in a daisy chain.

Each configuration pin D<sub>x</sub> (x=1-2) has additional circuitry to aid in the position detection.
# Switchable resistive pull-up to V<sub>bat</sub>
# Pull-down to GND
# Comparator referenced to V<sub>bat</sub>/2

==== XWDC auto-addressing procedure ====
At the start of the procedure no SNPD devices have a NAD assigned

1 First auto-addressing LIN message
:1.1 All outputs (D<sub>2</sub>) are set to a high level, all pull-downs are turned off
:1.2 The first SNPD node is selected. It is identified by having the input D<sub>1</sub> low (hardwired).
:1.3 The selected node takes the address from the LIN configuration message
:1.4 The detected node turns on the pull-down at the output D<sub>2</sub>
2 Subsequent auto-addressing LIN messages
:2.1 The first non addressed SNPD node is selected. It is identified by having the input D<sub>1</sub> low (D<sub>2</sub> of previous node).
:2.2 The selected node takes the address from the LIN configuration message
:2.3 The detected node turns on the pull-down at the output D<sub>2</sub>
:2.4 Steps 2.1-2.4 are repeated until all slave nodes are assigned an address
3 All pull-ups and pull-downs are turned off completing the addressing procedure

=== Bus shunt method (BSM) ===
Each slave node has two LIN pins
# bus_in
# bus_out

Each slave node needs some additional circuitry compared to the standard LIN circuitry to aid in the position detection.
# The standard pull-up must be switchable
# Switchable 2&nbsp;mA current source from V<sub>bat</sub>
# Shunt resistor
# Differential amplifier
# Analog to digital converter

==== BSM auto-addressing procedure ====
At the start of the procedure, none of the SNPD devices have a NAD assigned. The autoaddressing routine is performed during the sync field. The sync field is broken into three phases:

1 Offset current measurement
:1.1 All outputs pull-ups and current sources are switched off
:1.2 The bus current is measured, '''I<sub>offset</sub>'''
2 Pull-up mode
:2.1 Pull-ups are turned on and current sources remain off
:2.2 The bus current is measured, '''I<sub>PU</sub>'''
:2.3 Nodes with ΔI = '''I<sub>PU</sub>'''-'''I<sub>offset</sub>''' < 1&nbsp;mA are "selected"
3 Current source mode
:3.1 Selected nodes switch current source on and others switch pull-ups off
:3.2 Bus current is measured, '''I<sub>CS</sub>'''
:3.3 Node with ΔI = '''I<sub>CS</sub>'''-'''I<sub>offset</sub>''' < 1&nbsp;mA is detected as the last node
:3.4 Current sources are switched off and pull-ups are switched on
:3.5 The last node will accept the address contained in the LIN configuration message

This technique is covered by the patents EP 1490772 B1 and US 7091876.