ATMEGA324P-15MT1 Atmel, ATMEGA324P-15MT1 Datasheet - Page 39
![MCU AVR 32K FLASH 15MHZ 44-QFN](/photos/12/13/121316/313-44-qfn_sml.jpg)
ATMEGA324P-15MT1
Manufacturer Part Number
ATMEGA324P-15MT1
Description
MCU AVR 32K FLASH 15MHZ 44-QFN
Manufacturer
Atmel
Series
AVR® ATmegar
Specifications of ATMEGA324P-15MT1
Core Processor
AVR
Core Size
8-Bit
Speed
16MHz
Connectivity
I²C, SPI, UART/USART
Peripherals
Brown-out Detect/Reset, POR, PWM, WDT
Number Of I /o
32
Program Memory Size
32KB (16K x 16)
Program Memory Type
FLASH
Eeprom Size
1K x 8
Ram Size
2K x 8
Voltage - Supply (vcc/vdd)
2.7 V ~ 5.5 V
Data Converters
A/D 8x10b
Oscillator Type
Internal
Operating Temperature
-40°C ~ 105°C
Package / Case
44-VQFN
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
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7.12
7.12.1
7674F–AVR–09/09
Register Description
OSCCAL – Oscillator Calibration Register
When switching between prescaler settings, the System Clock Prescaler ensures that no
glitches occurs in the clock system. It also ensures that no intermediate frequency is higher than
neither the clock frequency corresponding to the previous setting, nor the clock frequency corre-
sponding to the new setting.
The ripple counter that implements the prescaler runs at the frequency of the undivided clock,
which may be faster than the CPU's clock frequency. Hence, it is not possible to determine the
state of the prescaler - even if it were readable, and the exact time it takes to switch from one
clock division to the other cannot be exactly predicted. From the time the CLKPS values are writ-
ten, it takes between T1 + T2 and T1 + 2 * T2 before the new clock frequency is active. In this
interval, 2 active clock edges are produced. Here, T1 is the previous clock period, and T2 is the
period corresponding to the new prescaler setting.
To avoid unintentional changes of clock frequency, a special write procedure must be followed
to change the CLKPS bits:
1. Write the Clock Prescaler Change Enable (CLKPCE) bit to one and all other bits in
2. Within four cycles, write the desired value to CLKPS while writing a zero to CLKPCE.
Interrupts must be disabled when changing prescaler setting to make sure the write procedure is
not interrupted.
• 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. A pre-programmed calibration value is
automatically written to this register during chip reset, giving the Factory calibrated frequency as
specified in
the oscillator frequency. The oscillator can be calibrated to frequencies as specified in
26-2 on page
Note that this oscillator is used to time EEPROM and Flash write accesses, and these write
times will be affected accordingly. If the EEPROM or Flash are written, do not calibrate to more
than 8.8 MHz. Otherwise, the EEPROM or Flash write may fail.
The CAL7 bit determines the range of operation for the oscillator. Setting this bit to 0 gives the
lowest frequency range, setting this bit to 1 gives the highest frequency range. The two fre-
quency ranges are overlapping, in other words a setting of OSCCAL = 0x7F gives a higher
frequency than OSCCAL = 0x80.
The CAL6..0 bits are used to tune the frequency within the selected range. A setting of 0x00
gives the lowest frequency in that range, and a setting of 0x7F gives the highest frequency in the
range.
Bit
(0x66)
Read/Write
Initial Value
CLKPR to zero.
Table 26-2 on page
331. Calibration outside that range is not guaranteed.
CAL7
R/W
7
CAL6
R/W
6
331. The application software can write this register to change
CAL5
R/W
5
Device Specific Calibration Value
CAL4
R/W
4
ATmega164P/324P/644P
CAL3
R/W
3
CAL2
R/W
2
CAL1
R/W
1
CAL0
R/W
0
OSCCAL
Table
39
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