AT94K05AL ATMEL Corporation, AT94K05AL Datasheet - Page 123

• Manufacturer Part Number: AT94K05AL
• Description: Fpslic Devices Combine 5K Gates of Atmel's Patented AT40K Fpga Architecture, a 20 Mips Avr 8-bit Risc Microprocessor Core, Numerous Fixed Microcontroller Peripheries And up to 36K Bytes of Program And Data SRAM.
• Manufacturer: ATMEL Corporation

Multi-processor
Communication Mode
UART Control
Rev. 1138F–FPSLI–06/02
The Multi-processor Communication Mode enables several Slave MCUs to receive data from
a Master MCU. This is done by first decoding an address byte to find out which MCU has been
addressed. If a particular Slave MCU has been addressed, it will receive the following data
bytes as normal, while the other Slave MCUs will ignore the data bytes until another address
byte is received.
For an MCU to act as a Master MCU, it should enter 9-bit transmission mode (CHR9n in UCS-
RnB set). The 9-bit must be one to indicate that an address byte is being transmitted, and zero
to indicate that a data byte is being transmitted.
For the Slave MCUs, the mechanism appears slightly different for 8-bit and 9-bit Reception
mode. In 8-bit Reception mode (CHR9n in UCSRnB cleared), the stop bit is one for an
address byte and zero for a data byte. In 9-bit Reception mode (CHR9n in UCSRnB set), the
9-bit is one for an address byte and zero for a data byte, whereas the stop bit is always High.
The following procedure should be used to exchange data in Multi-processor Communication
mode:
UART0 I/O Data Register – UDR0
UART1 I/O Data Register – UDR1
The UDRn register is actually two physically separate registers sharing the same I/O address.
When writing to the register, the UART Transmit Data register is written. When reading from
UDRn, the UART Receive Data register is read.
Bit
$0C ($2C)
Read/Write
Initial Value
Bit
$03 ($23)
Read/Write
Initial Value
1. All Slave MCUs are in Multi-processor Communication Mode (MPCMn in UCSRnA
2. The Master MCU sends an address byte, and all Slaves receive and read this byte.
3. Each Slave MCU reads the UDRn register and determines if it has been selected.
4. For each received data byte, the receiving MCU will set the receive complete flag
5. After the last byte has been transferred, the process repeats from step 2.
is set).
In the Slave MCUs, the RXCn flag in UCSRnA will be set as normal.
If so, it clears the MPCMn bit in UCSRnA, otherwise it waits for the next address
byte.
(RXCn in UCSRnA. In 8-bit mode, the receiving MCU will also generate a framing
error (FEn in UCSRnA set), since the stop bit is zero. The other Slave MCUs,
which still have the MPCMn bit set, will ignore the data byte. In this case, the UDRn
register and the RXCn, FEn, or flags will not be affected.
7
MSB
R/W
0
7
MSB
R/W
0
6
R/W
0
6
R/W
0
5
R/W
0
5
R/W
0
4
R/W
0
4
R/W
0
3
R/W
0
3
R/W
0
AT94K Series FPSLIC
2
R/W
0
2
R/W
0
1
R/W
0
1
R/W
0
0
LSB
R/W
0
0
LSB
R/W
0
UDR0
UDR1
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