ATmega8515 Atmel Corporation, ATmega8515 Datasheet - Page 138

• Manufacturer Part Number: ATmega8515
• Manufacturer: Atmel Corporation

Specifications of ATmega8515

• Flash (kbytes): 8 Kbytes
• Pin Count: 44
• Max. Operating Frequency: 16 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 16
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 35
• Ext Interrupts: 3
• Usb Speed: No
• Usb Interface: No
• Spi: 1
• Uart: 1
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Resistive Touch Screen: No
• Temp. Sensor: No
• Crypto Engine: No
• Sram (kbytes): 0.5
• Eeprom (bytes): 512
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -40 to 85
• I/o Supply Class: 2.7 to 5.5
• Operating Voltage (vcc): 2.7 to 5.5
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 2
• Output Compare Channels: 3
• Input Capture Channels: 1
• Pwm Channels: 3
• 32khz Rtc: No
• Calibrated Rc Oscillator: Yes

Internal Clock Generation –
The Baud Rate Generator
138
ATmega8515(L)
Signal description:
Internal clock generation is used for the asynchronous and the synchronous master
modes of operation. The description in this section refers to Figure 65.
The USART Baud Rate Register (UBRR) and the down-counter connected to it function
as a programmable prescaler or baud rate generator. The down-counter, running at sys-
tem clock (fosc), is loaded with the UBRR value each time the counter has counted
down to zero or when the UBRRL Register is written. A clock is generated each time the
cou nter rea ches zero. Th is clock is the bau d r ate gen erato r clock outp ut
(= fosc/(UBRR+1)). The Transmitter divides the baud rate generator clock output by 2,
8, or 16 depending on mode. The baud rate generator output is used directly by the
Receiver’s clock and data recovery units. However, the recovery units use a state
machine that uses 2, 8, or 16 states depending on mode set by the state of the UMSEL,
U2X, and DDR_XCK bits.
Table 60 contains equations for calculating the baud rate (in bits per second) and for
calculating the UBRR value for each mode of operation using an internally generated
clock source.
Table 60. Equations for Calculating Baud Rate Register Setting
Note:
Some examples of UBRR values for some system clock frequencies are found in Table
68 (see page 160).
Operating Mode
Asynchronous Normal mode
(U2X = 0)
Asynchronous Double Speed
mode (U2X = 1)
Synchronous Master mode
txclk
rxclk
xcki
xcko
fosc
BAUD Baud rate (in bits per second, bps)
f
UBRR Contents of the UBRRH and UBRRL Registers, (0-4095)
OSC
1. The baud rate is defined to be the transfer rate in bit per second (bps).
Transmitter clock. (Internal Signal)
Receiver base clock. (Internal Signal)
Input from XCK pin (internal Signal). Used for synchronous slave operation.
Clock output to XCK pin (Internal Signal). Used for synchronous master
operation.
XTAL pin frequency (System Clock).
System Oscillator clock frequency
BAUD
BAUD
BAUD
Equation for Calculating
Baud Rate
=
=
=
-------------------------------------- -
16 UBRR
---------------------------------- -
8 UBRR
---------------------------------- -
2 UBRR
(
(
(
f
f
f
OSC
OSC
OSC
(1)
+
+
+
1
1
1
)
)
)
Equation for Calculating
UBRR
UBRR
UBRR
UBRR Value
=
=
=
----------------------- - 1
16BAUD
------------------- - 1
8BAUD
------------------- - 1
2BAUD
2512K–AVR–01/10
f
f
f
OSC
OSC
OSC
–
–
–