ATMEGA323-8AC Atmel, ATMEGA323-8AC Datasheet - Page 91
![IC AVR MCU 32K 8MHZ COM 44TQFP](/photos/6/70/67042/313-44-tqfp_sml.jpg)
ATMEGA323-8AC
Manufacturer Part Number
ATMEGA323-8AC
Description
IC AVR MCU 32K 8MHZ COM 44TQFP
Manufacturer
Atmel
Series
AVR® ATmegar
Datasheet
1.ATMEGA323L-4PC.pdf
(247 pages)
Specifications of ATMEGA323-8AC
Core Processor
AVR
Core Size
8-Bit
Speed
8MHz
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)
4.5 V ~ 5.5 V
Data Converters
A/D 8x10b
Oscillator Type
Internal
Operating Temperature
0°C ~ 70°C
Package / Case
44-TQFP, 44-VQFP
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
Other names
ATMEGA3238AC
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Multi-processor
Communication Mode
Using MPCM
1457G–AVR–09/03
Setting the Multi-Processor Communication mode (MPCM) bit in UCSRA enables a fil-
tering function of incoming frames received by the USART Receiver. Frames that do not
contain address information will be ignored and not put into the receive buffer. This
effectively reduces the number of incoming frames that has to be handled by the CPU,
in a system with multiple MCUs that communicate via the same serial bus. The Trans-
mitter is unaffected by the MPCM setting, but has to be used differently when it is a part
of a system utilizing the Multi-processor Communication mode.
If the Receiver is set up to receive frames that contain 5 to 8 data bits, then the first stop
bit indicates if the frame contain data or address information. If the Receiver is set up for
frames with 9 data bits, then the ninth bit (RXB8) is used for identifying address and
data frames. When the frame type bit (the first stop or the ninth bit) is one, the frame
contains an address. When the frame type bit is zero the frame is a data frame.
The Multi-processor Communication mode enables several Slave MCUs to receive data
from a Master MCU. This is done by first decoding an address frame to find out which
MCU has been addressed. If a particular Slave MCU has been addressed, it will receive
the following data frames as normal, while the other Slave MCUs will ignore the
received frames until another address frame is received.
For an MCU to act as a Master MCU, it can use a 9-bit character frame format (UCSZ =
7). The ninth bit (TXB8) must be set when an address frame (TXB8 = 1) or cleared when
a data frame (TXB = 0) is being transmitted. The Slave MCUs must in this case be set to
use a 9-bit character frame format.
The following procedure should be used to exchange data in Multi-processor Communi-
cation mode:
1. All Slave MCUs are in Multi-processor Communication mode (MPCM in UCSRA
2. The Master MCU sends an address frame, and all Slaves Receive and read this
3. Each Slave MCU reads the UDR Register and determines if it has been
4. The addressed MCU will receive all data frames until a new address frame is
5. When the last data frame is received by the addressed MCU, the addressed
Using any of the 5- to 8-bit character frame formats is possible, but impractical since the
Receiver must change between using n and n+1 character frame formats. This makes
full-duplex operation difficult since the Transmitter and Receiver uses the same charac-
ter size setting. If 5- to 8-bit character frames are used, the Transmitter must be set to
use two stop bit (USBS = 1) since the first stop bit is used for indicating the frame type.
Do not use Read-Modify-Write instructions (SBI and CBI) to set or clear the MPCM bit.
The MPCM bit shares the same I/O location as the TXC Flag and this might accidentally
be cleared when using SBI or CBI instructions.
is set).
frame. In the Slave MCUs, the RXC Flag in UCSRA will be set as normal.
selected. If so, it clears the MPCM bit in UCSRA, otherwise it waits for the next
address byte and keeps the MPCM setting.
received. The other Slave MCUs, which still have the MPCM bit set, will ignore
the data frames.
MCU sets the MPCM bit and waits for a new address frame from Master. The
process then repeats from 2.
ATmega323(L)
91
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