Preliminary C8051F120/1/2/3 C8051F124/5/6/7 - KEMT FEI TUKE

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C8051F120/1/2/3 C8051F124/5/6/7 Preliminary 21.2. Multiprocessor Communications Modes 2 and 3 support multiprocessor communication between a master processor and one or more slave processors by special use of the ninth data bit and the built-in UART0 address recognition hardware. When a master processor wants to transmit to one or more slaves, it first sends an address byte to select the target(s). An address byte differs from a data byte in that its ninth bit is logic 1; in a data byte, the ninth bit is always set to logic 0. UART0 will recognize as “valid” (i.e., capable of causing an interrupt) two types of addresses: (1) a masked address and (2) a broadcast address at any given time. Both are described below. 21.2.1. Configuration of a Masked Address The UART0 address is configured via two SFR’s: SADDR0 (Serial Address) and SADEN0 (Serial Address Enable). SADEN0 sets the bit mask for the address held in SADDR0: bits set to logic 1 in SADEN0 correspond to bits in SADDR0 that are checked against the received address byte; bits set to logic 0 in SADEN0 correspond to “don’t care” bits in SADDR0. Example 1, SLAVE #1 Example 2, SLAVE #2 Example 3, SLAVE #3 SADDR0 = 00110101 SADDR0 = 00110101 SADDR0 = 00110101 SADEN0 = 00001111 SADEN0 = 11110011 SADEN0 = 11000000 UART0 Address = xxxx0101 UART0 Address = 0011xx01 UART0 Address = 00xxxxxx Setting the SM20 bit (SCON0.5) configures UART0 such that when a stop bit is received, UART0 will generate an interrupt only if the ninth bit is logic 1 (RB80 = ‘1’) and the received data byte matches the UART0 slave address. Following the received address interrupt, the slave will clear its SM20 bit to enable interrupts on the reception of the following data byte(s). Once the entire message is received, the addressed slave resets its SM20 bit to ignore all transmissions until it receives the next address byte. While SM20 is logic 1, UART0 ignores all bytes that do not match the UART0 address and include a ninth bit that is logic 1. 21.2.2. Broadcast Addressing Multiple addresses can be assigned to a single slave and/or a single address can be assigned to multiple slaves, thereby enabling "broadcast" transmissions to more than one slave simultaneously. The broadcast address is the logical OR of registers SADDR0 and SADEN0, and ‘0’s of the result are treated as “don’t cares”. Typically a broadcast address of 0xFF (hexadecimal) is acknowledged by all slaves, assuming “don’t care” bits as ‘1’s. The master processor can be configured to receive all transmissions or a protocol can be implemented such that the master/slave role is temporarily reversed to enable half-duplex transmission between the original master and slave(s).. Example 4, SLAVE #1 Example 5, SLAVE #2 Example 6, SLAVE #3 SADDR0 = 00110101 SADDR0 = 00110101 SADDR0 = 00110101 SADEN0 = 00001111 SADEN0 = 11110011 SADEN0 = 11000000 Broadcast Address = 00111111 Broadcast Address = 11110111 Broadcast Address = 11110101 Where all ZEROES in the Broadcast address are don’t cares. Note in the above examples 4, 5, and 6, each slave would recognize as “valid” an address of 0xFF as a broadcast address. Also note that examples 4, 5, and 6 uses the same SADDR0 and SADEN0 register values as shown in the examples 1, 2, and 3 respectively (slaves #1, 2, and 3). Thus, a master could address each slave device individually using a masked address, and also broadcast to all three slave devices. For example, if a Master were to send an address “11110101”, only slave #1 would recognize the address as valid. If a master were to then send an address of “11111111”, all three slave devices would recognize the address as a valid broadcast address. Page 258 DS008-0.8-AUG02 © 2002 Cygnal Integrated Products, Inc.
Preliminary C8051F120/1/2/3 C8051F124/5/6/7 Figure 21.7. UART Multi-Processor Mode Interconnect Diagram Master Device Slave Device Slave Device Slave Device +5V RX TX RX TX RX TX RX TX 21.3. Frame and Transmission Error Detection All Modes: The Transmit Collision bit (TXCOL0 bit in register SCON0) reads ‘1’ if user software writes data to the SBUF0 register while a transmit is in progress. Note that the TXCOL0 bit is also used as the SM20 bit when written by user software. Modes1,2,and3: The Receive Overrun bit (RXOVR0 in register SCON0) reads ‘1’ if a new data byte is latched into the receive buffer before software has read the previous byte. Note that the RXOVR0 bit is also used as the SM10 bit when written by user software. The Frame Error bit (FE0 in register SCON0) reads ‘1’ if an invalid (low) STOP bit is detected. Note that the FE0 bit is also used as the SM00 bit when written by user software. © 2002 Cygnal Integrated Products, Inc. DS008-0.8-AUG02 Page 259
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Preliminary C8051F120/1/2/3 C8051F124/5/6/7 - KEMT FEI TUKE

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