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Serial Communication I

Serial Communication I. Overview. Serial Transmission, UARTs System Management Bus a.k.a. SMB/I2C Serial Peripheral Interface Bus a.k.a. SPI. Serial Transmission of Data. parallel. receiver. sender. serial. sender. receiver. Serial Data Transmission. serial. Receiver must know

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Serial Communication I

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  1. Serial Communication I EE/CS-352: Embedded Microcontrollers Systems

  2. Overview • Serial Transmission, • UARTs • System Management Bus a.k.a. SMB/I2C • Serial Peripheral Interface Bus a.k.a. SPI EE/CS-352: Embedded Microcontrollers Systems

  3. Serial Transmission of Data parallel receiver sender ... serial sender receiver EE/CS-352: Embedded Microcontrollers Systems

  4. Serial Data Transmission serial • Receiver must know • when transmission begins • when transmission ends • if data was transferred correctly sender receiver EE/CS-352: Embedded Microcontrollers Systems

  5. Asynchronous Communication • Sender and receiver agree on a common data transfer rate (BAUD rate) Half-duplex (one way) sender receiver sender /receiver receiver /sender Full-duplex (two ways) EE/CS-352: Embedded Microcontrollers Systems

  6. Synchronous Serial Communication • Common clock between sender and receiver • In 8051 can implement synchronous serial communication with • UARTs • SMB – System Management Bus • SPI – Serial Peripheral Interface data sender clock receiver EE/CS-352: Embedded Microcontrollers Systems

  7. Serial Communication with 8051 • UART0 and UART1 • SPI – Serial Peripheral Interface • SMB – System Management Bus • In all of these subsystems, program writes data in parallel to a SFR, and the subsystem controls the serial transfer of data. EE/CS-352: Embedded Microcontrollers Systems

  8. Serial Transmission • Synchronous • common clock wire used to synchronize • data sent in multiple bytes (relatively fast) • Asynchronous • most widely used for PC communication • no common clock wire between sender/receiver • data sent in individual bytes • simple, high overhead, (relatively slow) First look at this EE/CS-352: Embedded Microcontrollers Systems

  9. A. Synchrononus Communication EE/CS-352: Embedded Microcontrollers Systems

  10. Synchronous Communication with UART EE/CS-352: Embedded Microcontrollers Systems

  11. Synchronous Communication with UART data RxD UART0 TxD clock EE/CS-352: Embedded Microcontrollers Systems

  12. UART0 Synchronous Mode • Can either transmit or receive. • Clock rate is fixed at SYSCLK/12 • Data transmission begins when an instruction writes a data byte to the SBUF0 register. • Data reception begins when the REN0 Receive Enable bit (SCON0.4) is set to logic 1 and the RI0Receive Interrupt Flag (SCON0.0) is cleared. EE/CS-352: Embedded Microcontrollers Systems

  13. Synchronous Serial Interface Data Transmission example – TO a shift register 8-bits are transferred, LSB first, and 8 clock cycles sent IN Note only TWO wires are needed – not 8 EE/CS-352: Embedded Microcontrollers Systems

  14. Synchronous Serial Interface Data Transmission example – FROM a shift register 8 clock cycles sent, 8-bits are transferred, LSB first OUT EE/CS-352: Embedded Microcontrollers Systems

  15. Serial Communication with System Management Bus (SMB) EE/CS-352: Embedded Microcontrollers Systems

  16. SMB – SMBus0 • 2-wire, bidirectional serial bus • Compliant with standards: • System Management Bus v1.1 • I2C serial bus • SMBus0 can operate as master or slave • SCL and SDA must be pulled high when bus is free Vdd serial data SDA SMBus0 serial clock SCL EE/CS-352: Embedded Microcontrollers Systems

  17. SMB Protocol • A typical SMBus transaction consists of: • a START condition followed by • an address byte (Bits7-1: 7-bit slave address; Bit0: R/W direction bit), • one or more bytes of instruction/data, and a • STOP condition. • Each byte that is received (by a master or slave) must be acknowledged (ACK) with a low SDA during a high SCL. • If the receiving device does not ACK, the transmitting device will read a “not acknowledge” (NACK), which is a high SDA during a high SCL. serial data SDA SMBus0 serial clock SCL EE/CS-352: Embedded Microcontrollers Systems

  18. SMBus0 – Typical Configuration Voltage levels somewhat flexible EE/CS-352: Embedded Microcontrollers Systems

  19. SMB – Timing Diagram • SMB protocol also specifies • arbitration • timeouts EE/CS-352: Embedded Microcontrollers Systems

  20. SMB0 Registers • SMB0CN Control Register • SMB0CR Clock Rate Register • SMB0ADR Address Register • SMB0DAT Data Register • SMB0STA Status Register EE/CS-352: Embedded Microcontrollers Systems

  21. SMB Registers: SMB0CN Control Register • BUSY – SMB status flag (1=busy, 0=free) • ENSMB – SMB enable (1=enable, 0=disable) • STA – SMB start flag (1=transmit start) • STO – SMB stop flag (1=transmit stop) • SI – SMB Serial Interrupt flag (must be cleared by software) • AA – SMB Assert Acknowledge flag (for sending “ack” or “nack” • FTE – Free Time Enable (1=disable on timeout) • TOE – Timeout Enable (1=enable timeout for SCL low) EE/CS-352: Embedded Microcontrollers Systems

  22. SMB Registers: SMB0CRClock Rate Register • Controls the SCL clock rate • Reloads an 8-bit counter that toggles SCL • Limit: SMB0CR < (288 - 0.85.SYSCLK)/1.125 • TLOW = (256 - SMB0CR)/SYSCLK • THIGH =(258- SMB0CR/SYSCLK) +625ns Example: for 2 MHz sysclk and SMB0CR=0: TLOW = 128us, THIGH = 129us EE/CS-352: Embedded Microcontrollers Systems

  23. SMB Registers: SMB0DAT DATA Register • Data shifted out (on SDA) MSB (bit 7) first EE/CS-352: Embedded Microcontrollers Systems

  24. SMB/I2C Protocol • The master initiates data transfer by establishing a START condition, which is a high-to-low transition on SDA while SCL is high • The following byte is the slave address byte, which consists of the slave address followed by an R/W bit (0=write, 1=read) • Slave must put ACK (low) on bus to acknowledge • The next byte (or more) is a data byte • Master sends a “STOP” signal at end of data data instruction 7-bit address ACK start R/W EE/CS-352: Embedded Microcontrollers Systems

  25. SMB/I2C Protocol on C8051F020 • Interrupts are generated after an action has been performed • There is a status code associated with each of the actions • In our code, we will poll to determine if the interrupt flag is set and this will allow us to move to the next stage EE/CS-352: Embedded Microcontrollers Systems

  26. SMB/I2C Protocol on C8051F020 Master Transmitter Mode EE/CS-352: Embedded Microcontrollers Systems

  27. Serial Port Pins • Crossbar used to route serial pins to Ports Serial pins connected to Port 0 UART has highest priority If UART, SPI, and SMB are all enabled, pins assigned as indicated EE/CS-352: Embedded Microcontrollers Systems

  28. Communicate Serially with a Resistor! EE/CS-352: Embedded Microcontrollers Systems

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