ATmega644PR231 Atmel Corporation, ATmega644PR231 Datasheet - Page 198
ATmega644PR231
Manufacturer Part Number
ATmega644PR231
Description
Manufacturer
Atmel Corporation
Specifications of ATmega644PR231
Flash (kbytes)
64 Kbytes
Max. Operating Frequency
20 MHz
Max I/o Pins
32
Spi
3
Twi (i2c)
1
Uart
2
Adc Channels
8
Adc Resolution (bits)
10
Adc Speed (ksps)
15
Analog Comparators
1
Crypto Engine
AES
Sram (kbytes)
4
Eeprom (bytes)
2048
Operating Voltage (vcc)
1.8 to 3.6
Timers
3
Frequency Band
2.4 GHz
Max Data Rate (mb/s)
2
Antenna Diversity
Yes
External Pa Control
Yes
Power Output (dbm)
3
Receiver Sensitivity (dbm)
-101
Receive Current Consumption (ma)
13.2
Transmit Current Consumption (ma)
14.4
Link Budget (dbm)
104
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17. USART in SPI Mode
17.1
17.2
17.3
8011O–AVR–07/10
Features
Overview
Clock Generation
•
•
•
•
•
•
•
•
The Universal Synchronous and Asynchronous serial Receiver and Transmitter (USART) can be
set to a master SPI compliant mode of operation.
Setting both UMSELn1:0 bits to one enables the USART in MSPIM logic. In this mode of opera-
tion the SPI master control logic takes direct control over the USART resources. These
resources include the transmitter and receiver shift register and buffers, and the baud rate gen-
erator. The parity generator and checker, the data and clock recovery logic, and the RX and TX
control logic is disabled. The USART RX and TX control logic is replaced by a common SPI
transfer control logic. However, the pin control logic and interrupt generation logic is identical in
both modes of operation.
The I/O register locations are the same in both modes. However, some of the functionality of the
control registers changes when using MSPIM.
The Clock Generation logic generates the base clock for the Transmitter and Receiver. For
USART MSPIM mode of operation only internal clock generation (that is master operation) is
supported. The Data Direction Register for the XCKn pin (DDR_XCKn) must therefore be set to
one (that is as output) for the USART in MSPIM to operate correctly. Preferably the DDR_XCKn
should be set up before the USART in MSPIM is enabled (that is TXENn and RXENn bit set to
one).
The internal clock generation used in MSPIM mode is identical to the USART synchronous mas-
ter mode. The baud rate or UBRRn setting can therefore be calculated using the same
equations, see
Table 17-1.
Operating Mode
Synchronous Master
mode
Full Duplex, Three-wire Synchronous Data Transfer
Master Operation
Supports all four SPI Modes of Operation (Mode 0, 1, 2, and 3)
LSB First or MSB First Data Transfer (Configurable Data Order)
Queued Operation (Double Buffered)
High Resolution Baud Rate Generator
High Speed Operation (fXCKmax = fCK/2)
Flexible Interrupt Generation
Equations for Calculating Baud Rate Register Setting
Table
17-1:
Equation for Calculating Baud
BAUD
=
Rate
-------------------------------------- -
2 UBRRn
(
(1)
f
OSC
ATmega164P/324P/644P
+
1
)
Equation for Calculating UBRRn
UBRRn
Value
=
------------------- - 1
2BAUD
f
OSC
–
198
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