Serial USART
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The serial USART
is used for full duplex (two-way) communication between a receiver and
transmitter. This is accomplished by equipping the ATmega16 with independent
hardware for the transmitter and receiver. The USART is typically used for
asynchronous communication. That is, there is not a common clock between the
transmitter and receiver to keep them synchronized with one another. To
maintain synchronization between the transmitter and receiver, framing start
and stop bits are used at the beginning and end of each data byte in a
transmission sequence.
The ATmega16
USART is quite flexible. It has the capability to be set to a variety of data
transmission rates known as the baud (bits per second) rate. The USART may
also be set for data bit widths of 5 to 9 bits with one or two stop bits.
Furthermore, the ATmega16 is equipped with a hardware-generated parity bit
(even or odd) and parity check
hardware at the receiver. A single parity bit allows for the detection of a
single bit error within a byte of data. The USART may also be configured to
operate in a synchronous mode.
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Serial Peripheral
Interface
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The ATmega16 SPI
can also be used for two-way serial communication between a transmitter and a
receiver. In the SPI system, the transmitter and receiver share a common
clock source. This requires an additional clock line between the transmitter
and receiver but allows for higher data transmission rates as compared with
the USART.
The SPI may be
viewed as a synchronous 16-bit shift register with an 8-bit half residing in
the transmitter and the other 8-bit half residing in the receiver. The
transmitter is designated the master because it provides the synchronizing
clock source between the transmitter and the receiver. The receiver is
designated as the slave.
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Two-Wire Serial
Interface
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The TWI subsystem
allows the system designer to network a number of related devices
(microcontrollers, transducers, displays, memory storage, etc.) together into
a system using a two-wire interconnecting scheme. The TWI allows a maximum of
128 devices to be connected together. Each device has its own unique address
and may both transmit and receive over the two-wire bus at frequencies up to
400 kHz. This allows the device to freely exchange information with other
devices in the network within a small area.
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Analog-to-Digital
Converter
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The ATmega16 is
equipped with an eight-channel ADC subsystem. The ADC converts an analog
signal from the outside world into a binary representation suitable for use
by the microcontroller. The ATmega16 ADC has 10-bit resolution. This means
that an analog voltage between 0 and 5 V will be encoded into one of 1024
binary representations between (000)16 and (3FF)16. This provides
the ATmega16 with a voltage resolution of approximately 4.88 mV.
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Saturday, August 4, 2012
Serial Communications in AVR
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