Rainbow Electronics ATmega64C1 - Manual (Page 255)

255
7647A–AVR–02/08
ATmega32/64/M1/C1
19. ISRC - Current Source
19.1 Features
• 100µA Constant current source
• ± 2% Absolute Accuracy
The ATmega32/64/M1/C1 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 serie with a
≤
0.5% tolerance is recom-
mended. To protect the device against big values, the ADC must be configured with AVcc 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 19-1. Current Source Block Diagram
19.2 Typical applications
19.2.1 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 applica-
tion supported by the LIN node. A full dynamic node configuration can be used to set-up the LIN
nodes in a cluster.
AVCC
AREF Internal Circuit
External
Resistor
ISRCEN
AREF / ISRC
100 uA
AREFEN
ADC Input