Hệ thống nhúng - Chương 6 pdf

Flight plan • In this lesson we will review a couple of communication peripherals available in all the general-purpose devices in the new PIC24 family.. • Asynchronous serial communica

Hệ thống nhúng

Thạc sĩ Lê Mạnh Hải

Embedded Systems

Lesson 6 :Communication

Motivation:

• Synchronous serial interfaces

• Asynchronous serial interfaces

• Parallel interfaces

• Synchronous communication using the SPI modules

• Testing the Read Status Register command

• Writing to the EEPROM

• Reading the memory contents

• A nonvolatile storage library

• Testing the new NVM library

Flight plan

• In this lesson we will review a couple of

communication peripherals available in all the

general-purpose devices in the new PIC24 family

• Asynchronous serial communication interfaces

UART1 and UART2,

• Synchronous serial communication interfaces SPI1

and SPI2, comparing their relative strengths and limitations for use in embedded-control

applications.

Preflight checklist

• MPLAB® IDE,

• MPLAB C30 compiler and the

• MPLAB SIM simulator,

• Explorer16 demonstration board and the

• MPLAB ICD2 In Circuit Debugger

The flight

• The PIC24FJ128GA010 offers seven

communication peripherals that are designed to assist in all common embedded-control

applications.

– 2 × the universal asynchronous receiver and

transmitters (UARTs) – 2 × the SPI synchronous serial interfaces

– 2 × the I2C™ synchronous serial interfaces

Synchronous serial interfaces

Sharing an SPI bus among multiple masters is

theoretically possible but practically very rare

The main advantages of the SPI interface are truly

its simplicity and the speed that can be one order

of magnitude higher than that of the fastest I2C

bus (even without taking into consideration the

details of the protocol- specifi c overhead)

Asynchronous serial interfaces

The synchronization between transmitter and

receiver is obtained by extracting timing information

from the data stream itself Start and stop bits are

added to the data and precise formatting (with a fi

xed baud rate) allow reliable data transfer

9

Parallel interfaces

• The Parallel Master Port (PMP) completes the list of

basic communication interfaces of the PIC24.

• The PMP has the ability to transfer up to 8 bits of

information at a time while providing several address lines

– Interface directly to most LCD display modules commercially

available (alphanumeric and graphic modules with integrated controller)

– Compact Flash memory cards (or CF-I/O devices),

– printer ports and an almost infi nite number of other basic 8-bit

parallel devices available on the market and featuring the standard control signals: −CS, −RD, −WR.

Synchronous communication using

the SPI modules

• The SPI interface is essentially composed of

an 8-bit shift register: bits are

simultaneously shifted in (MSB fi rst) from the SDI line and shifted out from the SDO line in sync with the clock on pin SCK.

SPI Programming

1 #define SPI_MASTER 0x0120 // select 8-bit master mode, CKE=1, CKP=0

2 #define SPI_ENABLE 0x8000 // enable SPI port, clear status

3 #define CSEE _RD12 // select line for Serial EEPROM

4 #define TCSEE _TRISD12 // tris control for CSEE pin

5 // 1 init the PIC24 SPI peripheral

6 TCSEE = 0; // make SSEE pin output

7 CSEE = 1; // de-select the Serial EEPROM (low power standby)

8 SPI2CON1 = SPI_MASTER; // select mode

9 SPI2STAT = SPI_ENABLE; // enable the peripheral

10 // send one byte of data and receive one back at the same time

11 int writeSPI2( int data)

12 {

13 SPI2BUF = data; // write to buffer for TX

14 while( !SPI2STATbits.SPIRBF); // wait for transfer to complete

15 return SPI2BUF; // read the received value

16 }//writeSPI2

25LC256 Memory

1 // 25LC256 Serial EEPROM commands

2 #define SEE_WRSR 1 // write status register

3 #define SEE_WRITE 2 // write command

4 #define SEE_READ 3 // read command

5 #define SEE_WDI 4 // write disable

6 #define SEE_STAT 5 // read status register

7 #define SEE_WEN 6 // write enable

5 // I/O defi nitions

6 #define CSEE _RD12 // select line for Serial EEPROM

7 #define TCSEE _TRISD12 // tris control for CSEE pin

8 // peripheral confi gurations

9 #define SPI_MASTER 0x0120 // select 8-bit master mode, CKE=1, CKP=0

10 #define SPI_ENABLE 0x8000 // enable SPI port, clear status

11 // 25LC256 Serial EEPROM commands

12 #define SEE_WRSR 1 // write status register

13 #define SEE_WRITE 2 // write command

14 #define SEE_READ 3 // read command

15 #define SEE_WDI 4 // write disable

16 #define SEE_STAT 5 // read status register

17 #define SEE_WEN 6 // write enable

18 // send one byte of data and receive one back at the same time

19 int writeSPI2( int data)

20 {

21 SPI2BUF = data; // write to buffer for TX

22 while( !SPI2STATbits.SPIRBF); // wait for transfer to complete

23 return SPI2BUF; // read the received value

24 }//writeSPI2

1 main()

2 {

3 int i;

4 // 1 init the SPI peripheral

5 TCSEE = 0; // make SSEE pin output

6 CSEE = 1; // de-select the Serial EEPROM

7 SPI2CON1 = SPI_MASTER; // select mode

8 SPI2STAT = SPI_ENABLE; // enable the peripheral

9 // 2 Check the Serial EEPROM status

10.CSEE = 0; // select the Serial EEPROM

11.writeSPI2( SEE_STAT); // send a READ STATUS COMMAND

12.i = writeSPI2( 0); // send dummy, read data

13.CSEE = 1; // terminate command <-set brkpt here

14.} // main

• // I/O defi nitions for PIC24 + Explorer16 demo board

• #define CSEE _RD12 // select line for Serial EEPROM

• #define TCSEE _TRISD12 // tris control for CSEE pin

• //

1 void InitNVM(void)

2 {

3 // init the SPI peripheral

4 TCSEE = 0; // make SSEE pin output

5 CSEE = 1; // de-select the Serial EEPROM

6 SPI2CON1 = SPI_MASTER; // select mode

7 SPI2STAT = SPI_ENABLE; // enable the peripheral

8 }//InitNVM

9 int writeSPI2( int data)

10 {// send one byte of data and receive one back at the same time

11 SPI2BUF = data; // write to buffer for TX

12 while( !SPI2STATbits.SPIRBF); // wait for transfer to complete

13 return SPI2BUF; // read the received value

14 }//WriteSPI2

15 int ReadSR( void)

16 {// Check the Serial EEPROM status register

17 int i;

18 CSEE = 0; // select the Serial EEPROM

19 WriteSPI2( SEE_STAT); // send a READ STATUS COMMAND

20 i = WriteSPI2( 0); // send/receive

21 CSEE = 1; // deselect to terminate command

22 return i;

23 } //ReadSR

// increment current value

Nop(); // <-set brkpt here

Post-flight briefing

In this lesson we have seen briefl y how to use the SPI peripheral module, in its simplest configuration, to gain access to a 25LC256 Serial EEPROM memory, one of the most common types of nonvolatile memory

peripherals used in embedded-control applications.

Exercises

• Develop (circular) buffered versions of the

read and write functions.

• Enable the new SPI 16-bit mode to

accelerate basic read and write operation.

• Several functions in the library are

performing locking loops that could

reduce the overall application

performance By utilizing the SPI port

interrupts implement a non blocking

version of the library.

What to read at home?

CHAPTER 8: Asynchronous communication (pg 104 – pg125)

– UART configuration

– Sending and receiving data

– Testing the serial communication routines

– Building a simple console library

– Testing a VT100 terminal

– Using the serial port as a debugging tool

– The matrix

23

Next: Glass bliss

• HD44780 controller compatibility

• The Parallel Master Port

• Configuring the PMP for LCD module

control

• A small library of functions to access an

LCD display

• Advanced LCD control