Using the ATAVRAUTO100
2-7 ATAVRAUTO100 User Guide
7697B–AUTO–09/07
2.2 Power Supply
The o n-b oar d p ow er sup ply m ust be pr ov ide d v ia th e L IN co nne cto r. The
ATAVRAUTO100 has been designed for operating voltage from 7V to +18V wi th typical
voltage at 12V. The LIN transceiver ATA6621, connected to the LIN network, ha s an
internal vo ltage regulator which outputs 5.0V ±3%. Th is voltage is used to pow er the
AT90CAN128 device.
Figure 2-2. The LIN power line is used to bias the ATAVRAUTO100
Note: A LIN network has to be connected to have your LIN interface working (Input
supply from 7 to 18V DC).
2.3 Oscillator Sources
The ATAVRAUTO100 allows two oscillator sources:
Internal RC oscillator
External crystal (Default setting configuration)
2.3.1 Internal RC
oscillator
The calibrated in ternal RC Oscillator pro vides a fixed 8.0 MH z clock. The frequency is
nominal value at 3V and 25°C. If 8 MHz frequency exceeds the speci fication o f the
device (depends on VCC), the CKDIV8 fuse must be programmed in order to divide the
internal frequency by 8 during start-up. The device is shipped with the CKDIV8 fuse pro-
grammed. See “ System Clock Prescaler ” on page 41 for more details. Thi s clock may
be selected as the system clock by programming the CKSEL fuses as shown in Table
11. If selected, it will operate with no external components. During reset, hardware loads
the calibration byte into the OSCCAL Register and thereb y automatically calibrates the
RC Oscill ator. At 5V and 25°C, this cal ibration giv es a freque ncy within ±10% of the
nominal frequen cy. Using calibrati on methods as des cribed in applicati on notes avail-
able at www .atmel.com/avr it is possible to achieve ± 2% acc uracy at any g iven VCC
and temperature. When this Oscillator is used as the chip clock, the Watchdog Oscillator
will still be used for the Watchdog Timer and for the Reset Time-out.
Note: The internal RC oscillator can not be used to operate the ATAVRAUTO100 fo r
CAN operations. Only LIN Slave mode with a run-time oscillator calibration can
be used with the internal RC oscillator.