asynchronous serial i/o unit 12 - part 1. sci registers – channel 0 sci0bdh – sci baud rate...
TRANSCRIPT
Asynchronous Serial I/O
Unit 12 - Part 1
SCI Registers – Channel 0
• SCI0BDH – SCI Baud Rate Register High Byte• SCI0BDL – SCI Baud Rate Register Low Byte• SCI0CR1 – SCI Control Register 1• SCI0CR2 – SCI Control Register 2• SCI0SR1 – SCI Status Register 1• SCI0SR2 – SCI Status Register 2• SCI0DRH – SCI Data Register High Byte• SCI0DRL – SCI Data Register Low Byte
SCI Register DefinitionsChannel 0
#define SCI0BDH _P(0xC8)#define SCI0BDL _P(0xC9#define SCI0CR1 _P(0xCA)#define SCI0CR2 _P(0xCB)#define SCI0SR1 _P(0xCC)#define SCI0SR2 _P(0xCD)#define SCI0DRH _P(0xCE)#define SCI0DRL _P(0xCF)
Baud Rate Generation
BAUD RATE = 2 MHZ 16 * (BAUD RATE DIVISOR)
THEREFORE,
SET BAUD RATE DIVISOR = 2MHZ 16 * (DESIRED BAUD RATE)
Example – Baud Rate Initialization
Let Desired Baud = 9600
Using formula:Baud Rate Divisor = 2000000 16*9600
= 13.0208
(Use integer value of 13)
Register Initialization: SCIOBDH= 0SCIOBDL=13
(Max value of Baud Rate Divisor = 213 - 1 = 8192
Parity Type1: Odd0: Even
Parity Enable
0: 9 data bits1: 8 data bits
Select Loop-BackMode
Wake-up Condition Selection
Interrupt Enables Transmitter and Receiver Enables
Enter Sleep Mode
Send Break Character
Break Character
• Start Bit = “0”
• All Data Bits = “0”
• Parity Bits if present = “0”
• Stop Bit = “0”
• 68HC12 keeps line in “0” for additional bit times
Example: Initialize SCI Channel 0 /* Baud = 9600 */int divisor = 125000/9600; // divisor = 13SCI0BDH = divisor>>8; // SCIOBDH= 0 SCI0BDL = divisor; // SCIOBDL=13
/* Standard OperationM=0 – 8 data bitsPE =0 – No Parity PT =0 – Parity type*/
SCI0CR1 = 0x00;
/* TE = 1 – Enable TransmitterRE = 1 – Enable Receiver */
SCI0CR2 = 0x0C;
Parity Type1: Odd0: Even
Parity Enable
0: 9 data bits1: 8 data bits
Select Loop-BackMode
Wake-up Condition Selection(repeated slide)
Interrupt Enables Transmitter and Receiver Enables
Enter Sleep Mode
Send Break Character
(repeat slide)
Serial I/O Procedures
/* Receive a Character */unsigned char ci(void) {while((SCI0SR1&0x20)==0); return SCI0DRL; }
Checking RDEF flag
(repeated slide)
Serial I/O Procedure
/* Transmit a Character */void co(unsigned char c) {while((SCI0SR1&80)==0); SCI0DRL=c; }
Checking TDRE flag