Datasheet

23. ISRC - Current Source
23.1. Features
• 100μA constant current source
• ±2% absolute accuracy
The Atmel ATmega16M1/32M1/64M1 features a 100μA ±2% current source. After RESET or up on
request, the current is flowing through an external resistor. The voltage can be measured on the
dedicated pin shared with the ADC. Using a resistor in series with a ≤0.5% tolerance is recommended. To
protect the device against big values, the ADC must be configured with AV
CC
as internal reference to
perform the first measurement. Afterwards, another internal reference can be chosen according to the
previous measured value to refine the result. When ISRCEN bit is set, the ISRC pin sources 100μA.
Otherwise this pin keeps its initial function.
Figure 23-1. Current source block diagram

AVCC
AREF internal circuit
External
resistor
ISRCEN
AREF / ISRC
100uA
AREFEN
ADC input
23.2. Typical Applications
23.2.1. LIN Current Source
During the configuration of a LIN node in a cluster, it may be necessary to attribute dynamically an unique
physical address to every cluster node. The way to do it is not described in the LIN protocol.
The Current Source offers an excellent solution to associate a physical address to the application
supported by the LIN node. A full dynamic node configuration can be used to set-up the LIN nodes in a
cluster.
Atmel ATmega16M1/32M1/64M1 proposes to have an external resistor used in conjunction with the
Current Source. The device measures the voltage to the boundaries of the resistance via the Analog to
Atmel ATmega16M1/32M1/64M1 [DATASHEET]
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