AT90CAN128-16AI Atmel, AT90CAN128-16AI Datasheet - Page 179

• Manufacturer Part Number: AT90CAN128-16AI
• Description: IC MCU AVR FLASH 128K 64TQFP
• Manufacturer: Atmel
• Series: AVR® 90CANr

Specifications of AT90CAN128-16AI

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 16MHz
• Connectivity: CAN, EBI/EMI, I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 53
• Program Memory Size: 128KB (128K x 8)
• Program Memory Type: FLASH
• Eeprom Size: 4K x 8
• Ram Size: 4K x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 64-TQFP, 64-VQFP
• For Use With: ATDVK90CAN1 - KIT DEV FOR AT90CAN128 MCU
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

17.4
17.4.1
7679H–CAN–08/08
Clock Generation
Internal Clock Generation – Baud Rate Generator
The Clock Generation logic generates the base clock for the Transmitter and Receiver. The
USARTn supports four modes of clock operation: Normal asynchronous, Double Speed asyn-
chronous, Master synchronous and Slave synchronous mode. The UMSELn bit in USARTn
Control and Status Register C (UCSRnC) selects between asynchronous and synchronous
operation. Double Speed (asynchronous mode only) is controlled by the U2Xn found in the
UCSRnA Register. When using synchronous mode (UMSELn = 1), the Data Direction Register
for the XCKn pin (DDR_XCKn) controls whether the clock source is internal (Master mode) or
external (Slave mode). The XCKn pin is only active when using synchronous mode.
Figure 17-2
Figure 17-2. USARTn Clock Generation Logic, Block Diagram
Signal description:
Internal clock generation is used for the asynchronous and the synchronous master modes of
operation. The description in this section refers to
The USARTn Baud Rate Register (UBRRn) and the down-counter connected to it function as a
programmable prescaler or baud rate generator. The down-counter, running at system clock
(
when the UBRRnL Register is written. A clock is generated each time the counter reaches zero.
This clock is the baud rate generator clock output (=
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
f
clk
io
), is loaded with the UBRRn value each time the counter has counted down to zero or
txn clk
rxn clk
xn cki
xn cko
f
clk
DDR_XCKn
XCKn
io
Pin
shows a block diagram of the clock generation logic.
xn cko
xn cki
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.
System I/O Clock frequency.
clk
Down-Counter
io
Prescaling
Register
UBRRn
Sync
UBRRn+1
f
clk
UCPOLn
Detector
io
Edge
/2
Figure
f
clk
io
17-2.
/(UBRRn+1)). The Transmitter divides
/4
AT90CAN32/64/128
/2
DDR_XCKn
U2Xn
0
1
0
1
0
1
1
0
UMSELn
txn clk
rxn clk
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