AT90PWM2B-16SU View Datasheet(PDF) - Atmel Corporation

Part Name

Description

Manufacturer

AT90PWM2B-16SU

8-bit Atmel Microcontroller with 8K Bytes In-System Programmable Flash

Atmel Corporation 

4317K–AVR–03/2013

AT90PWM2/3/2B/3B

This clock may be selected as the system clock by programming the CKSEL Fuses as shown in

Table 7-6. If selected, it will operate with no external components. During reset, hardware loads

the pre-programmed calibration value into the OSCCAL Register and thereby automatically cal-

ibrates the RC Oscillator. The accuracy of this calibration is shown as Factory calibration in

Table 26-1 on page 303.

By changing the OSCCAL register from SW, see “Oscillator Calibration Register – OSCCAL” on

page 34, it is possible to get a higher calibration accuracy than by using the factory calibration.

The accuracy of this calibration is shown as User calibration in Table 26-1 on page 303.

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. For more information on the pre-programmed cali-

bration value, see the section “Calibration Byte” on page 284.

Table 7-6. Internal Calibrated RC Oscillator Operating Modes(1)(2)

Frequency Range (MHz)

CKSEL3..0

7.3 - 8.1

0010

Notes: 1. The device is shipped with this option selected.

2. If 8 MHz frequency exceeds the specification of the device (depends on VCC), the CKDIV8

Fuse can be programmed in order to divide the internal frequency by 8.

When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in

Table 7-7 on page 34.

Table 7-7. Start-up times for the internal calibrated RC Oscillator clock selection

Power Conditions

BOD enabled

Start-up Time from Power-

down and Power-save

6 CK

Additional Delay from

Reset (VCC = 5.0V)

14CK(1)

Fast rising power

Slowly rising power

6 CK

6 CK

14CK + 4.1 ms

14CK + 65 ms(1)

Reserved

SUT1..0

00

01

10

11

Note:

1. If the RSTDISBL fuse is programmed, this start-up time will be increased to

14CK + 4.1 ms to ensure programming mode can be entered.

2. The device is shipped with this option selected.

Table 7-8. Oscillator Calibration Register – OSCCAL

Bit

Read/Write

Initial Value

7

CAL7

R/W

6

CAL6

R/W

5

4

3

2

CAL5

CAL4

CAL3

CAL2

R/W

R/W

R/W

R/W

Device Specific Calibration Value

1

CAL1

R/W

0

CAL0

R/W

OSCCAL

• Bits 7..0 – CAL7..0: Oscillator Calibration Value

The Oscillator Calibration Register is used to trim the Calibrated Internal RC Oscillator to

remove process variations from the oscillator frequency. The factory-calibrated value is automat-

ically written to this register during chip reset, giving an oscillator frequency of 8.0 MHz at 25°C.

The application software can write this register to change the oscillator frequency. The oscillator

can be calibrated to any frequency in the range 7.3 - 8.1 MHz within ±1% accuracy. Calibration

outside that range is not guaranteed.

34

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