MC9S12单片机原理及嵌入式应用开发技术(6)-第5章-单片机串行通信模块(SCI)(实验4-SCI)课件

1、College of Communication Engineering, Jilin University第5章 单片机串行通信模块2College of Communication Engineering, Jilin University5.3 异步串行通信接口SCI模块5.3.1 异步串行通信协议RS-232标准5.3.2 SCI功能简介5.3.3 SCI寄存器5.3.4 SCI应用程序范例3College of Communication Engineering, Jilin University5.3.1 异步串行通信协议RS-232标准串行通信示意图4College of Com

2、munication Engineering, Jilin University5.3.1 异步串行通信协议RS-232标准EIA RS-232-C（CCITT V.24） 美国电子工业协会正式公布的异步串行通信标准，也是目前最常用的异步串行通信标准，用来实现计算机与计算机之间、计算机与外设之间的数据通信 RS-232-C电平采用负逻辑，即：逻辑1：-3-15V, 逻辑0：+3+15V （需要电平转换）RS-232-C接口标准有22根线，采用标准25芯D型插头座；PC上使用简化的9芯D型插座 多种通信应答（握手）方式： 硬件握手，自应答，XON/XOFF模式波特率： 300bps 20Kbps

3、， 物理层有多种实现方式（铜缆，光缆，红外，微波）起始位/停止位/数据位/奇偶校验/全双工半双工模式 广泛应用：Modem，20mA电流环，RS485 个人计算机都有标准的RS232接口，驱动程序，超级终端5College of Communication Engineering, Jilin University5.3.1 异步串行通信协议RS-232标准简化的9芯D型 DTE：数据终端设备，指PC或终端 DCE：数据通信设备，指调制解调器等外设DCE（母）DTE（公）6College of Communication Engineering, Jilin University5.3.1 异

4、步串行通信协议RS-232标准 简化的9芯D型接头信号定义（硬件流量控制） DTE DCE 3 TxD out TxD Transmit Data2 RxD in RxD Receive Data5 GND GND 7 RTS out RTS Require To Send8 CTS in CTS Clear To Send6 DSR in DSR Data Set Ready9 DCD in DCD Data Care Detected4 DTR out DTR Data Terminal Ready7College of Communication Engineering, Jilin U

5、niversity5.3.1 异步串行通信协议RS-232标准简化的9芯D型接头信号定义（自应答方式）DTE / DCE 2 TxD out TxD (Transmit Data )3 RxD in RxD (Receive Data)7 GND GND (Ground)4 RTS out RTS (Require to Send)5 CTS in CTS (Clear to Send)6 DSR in DSR (Data Terminal Ready)8 DCD in DCD (Data Carry Detected)20 DTR out DTR (Data Set Ready)Ready

6、always, or XON/XOFF protocol, ASCII only!8College of Communication Engineering, Jilin University5.3.1 异步串行通信协议RS-232标准简化的9芯D型接头信号定义（无应答方式）DTE / DCE 2 TxD out TxD (Transmit Data )3 RxD in RxD (Receive Data)7 GND GND (Ground)4 RTS out RTS (Require to Send)5 CTS in CTS (Clear to Send)6 DSR in DSR (Data

7、 Terminal Ready)8 DCD in DCD (Data Carry Detected)20 DTR out DTR (Data Set Ready)No Handshake, should use XON/XOFF protocol,ASCII only9College of Communication Engineering, Jilin University5.3.1 异步串行通信协议RS-232标准TTL level vs. RS232 level10College of Communication Engineering, Jilin University5.3.1 异步

8、串行通信协议RS-232标准TTL level vs. RS232 level11College of Communication Engineering, Jilin University5.3.1 异步串行通信协议RS-232标准RS232标准（1962）出现的比TTL（1964）还早；需要接口转换芯片MAX232MicrocontrollerDB9TTL/CMOSRS232双通道12College of Communication Engineering, Jilin University5.3.1 异步串行通信协议RS-232标准非归零码：NRZ (not return zero) e

9、ncoding参数：Several configurable parametersBaud rate, # start bits，#data bits, parity, #stop bits（波特率，起始位，数据位，奇偶校验位，停止位）Nomenclature: 9600，N81（无奇偶校验，8位数据，1位停止位）最低位：LSB- Least significant bit最高位：MSB- Most significant bit帧格式（Frame format）012345678LSBMSBstopidleidlestartParity(stop)13College of Communica

10、tion Engineering, Jilin University5.3.1 异步串行通信协议RS-232标准数据位识别接收端在其时钟上升沿采样数据线电平，以识别数据位的高低状态。What is the data transmitted above?14College of Communication Engineering, Jilin University5.3.1 异步串行通信协议RS-232标准Tx_clkRx_clkTxDRxD传输过程会引起信号的延迟，会引入外部干扰导致的噪声及毛刺数据位识别15College of Communication Engineering, Jilin

11、 University5.3.1 异步串行通信协议RS-232标准数据位识别- 通信双方有约定的通信速率（波特率）- 接收端按照16倍波特率的频率对信号进行高速采样 - 使用其中3个采样结果（7、8、9或8、9、10），通过3取2的机制确定实际的 信号电平状态- 如果3个采样结果不一致，noise标志会置起- 接收端在总线进入空闲状态后，通过监测下降沿，启动对起始位的判断，从而 开始整个数据帧的接收。16College of Communication Engineering, Jilin University5.3.1 异步串行通信协议RS-232标准波特率： bits per second

12、 Question1: 按照9600，N81的通信参数，每秒可以传送多少个字节？Hints: dont forget the start/stop bits.Question2: 对于一个总线频率为16MHz的微控制器，其SCI最高支持的波特率是多少？17College of Communication Engineering, Jilin University5.3.2 SCI功能简介发送和接收都具有双缓冲结构 CPU不能读写移位缓冲寄存器CPU仅能访问数据寄存器SCI 双缓冲寄存结构Transmitter: Receiver:TDR BUFFERSHIFT REGISTERDATA IND

13、ATAOUTT8PARITYGEN.DATA OUTRDR BUFFERSHIFT REGISTERDATAINR8PARITYCHECK18College of Communication Engineering, Jilin University5.3.2 SCI功能简介SCI 双缓冲寄存结构发送时，数据自动从数据寄存器转移到移位寄存器接收时，数据自动从移位寄存器转移到数据寄存器发送和接收的数据寄存器使用相同的寄存器地址 读写该寄存器地址具有不同的含义!Question: whats the function of the instructions below while(1) asm L

14、DAA SCI0DR asm STAA SCI0DR 19College of Communication Engineering, Jilin University5.3.2 SCI功能简介Tx data registerTx clock genNote the 16Shift registerParity genInterrupt request genControl logic20College of Communication Engineering, Jilin University5.3.3 SCI寄存器SCIBDH/L - SCI Baud Rate Control Regist

15、erBus clock1 819124M bus clockExercise1: 9600bps wanted， BR = ? BDH = ? BDL = ?Exercise2： the maximum baud rate = ?必须连续写入BDH和BDL寄存器，仅仅写入BDH没有作用。BR为0，表示SCI停止工作，以便节省电能。21College of Communication Engineering, Jilin University5.3.3 SCI寄存器SCCR1 - SCI Control Register 11 = EVEN PARITY0 = ODD PARITY1 = PAR

16、ITY Enabled0 = PARITY Disabled 1 = 9-BIT DATA 0 = 8-BIT DATA22College of Communication Engineering, Jilin University5.3.3 SCI寄存器SCICR 2 - SCI Control Register 2TE _ Transmitter Enable 1 = Transmitter Enabled0 = Transmitter DisabledRE Receiver Enable1 = Receiver Enabled0 = Receiver DisabledTCIE - Tra

17、nsmit Complete Interrupt Enable1 = Transmitter Complete IRQ Enabled0 = Transmitter Complete IRQ DisabledRIE - Receiver Interrupt Enable1 = Receiver IRQ Enabled0 = Receiver IRQ DisabledTIE - Transmitter Interrupt Enable1 = Transmitter IRQ Enabled0 = Transmitter IRQ Disabled23College of Communication

18、Engineering, Jilin University5.3.3 SCI寄存器SCISR 1 - SCI Status Register 1SCISR 2 - SCI Status Register 2RDRF: Receive data Register FullTC : Transmit CompleteTDRE: Transmit data register empty24College of Communication Engineering, Jilin University5.3.3 SCI寄存器SCIDRH/L - SCI Data Register High/LowNote

19、: R8 and T8 are used when 9-bit char is requiredNotice: same register for both transmit data and receive dataT825College of Communication Engineering, Jilin University5.3.4 SCI应用程序范例SCI模块编程方法SCI初始化：写SCI0BDH和SCI0BDL 设定SCI波特率；写控制寄存器SCI0CR2，设定中断允许位，并使能发送和接收SCI收发数据：通过查询SCI0SR1中的状态位或采用中断方式，读写数据寄存器，完成数据收发。26College of Communication Engineering, Jilin University5.3.4 SCI应用程序范例/SCI初始化函数void SCI0_Init(void) SCI0BDH = 0; SCI0BDL = 52; / bus freq = 8MHz，9600bps SCI0CR2 = 0 x0C;/允许发送和接收/SCI发送一个字节的函数（参数：c 为待发送的1字节数据）void Put_C