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INFORMATICA

INDUSTRIALE

Lezione 5

Prof. Christian Forlaniforlani@disco.unimib.it

Lezione 5 2

Informatica Industriale

Device Structure:

Peripherals

» I/O

» Parallel Slave Port (PSP)

» Timer

» Capture/Compare/PWM (CCP)

» Serial Slave Port (SSP)

» Master Synchronous Serial Port (MSSP)

» Addressable USART

» CAN

» Comparator Voltage Reference

» 10-bit A/D Converter

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Lezione 5 3

Informatica Industriale

PIC-USART MODULE(Universal Synchronous Asynchronous Receiver Transmitter)

• Full-duplex Asynchronous Or Half-duplex Synchronous

• 9-bit Addressable mode

• Double-buffered transmit and receive buffers

• Separate transmit and receive interrupts

• Dedicated baud rate generator

Lezione 5 4

Informatica Industriale

RS232 (http://www.tanzilli.com)Cos'e' e a cosa serve l'RS232

• Lo standard RS232 definisce una serie di specifiche per la trasmissione seriale di dati tra due dispositivi denominati DTE (Data Terminal Equipment) e DCE (Data Communication Equipment). Come si può vagamente intuire dal nome, il Data Communication Equipment e' un dispositivo che si occupa di gestire una comunicazione dati mentre il Data Terminal Equipment e' un dispositivo che si occupa di generare o ricevere dati.

La comunicazione seriale asincrona

• Per consentire la trasmissione di dati tra il PC ed il modem, lo standard RS232 definisce una serie di specifiche elettriche e meccaniche. Una di queste riguarda il tipo di comunicazione seriale che si vuole implementare che può essere sincrona o asincrona. Nel nostro caso analizzeremo solo la comunicazione seriale asincrona.

RS232 RS232

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Lezione 5 5

Informatica Industriale

Standard RS232RS232 Voltage levelsTTL Voltage levels

5V

0V

Logic ‘0’

Logic ‘1’

Codifica seriale del numero 48 = 0b00110000

a 9600 bps (RS-232 8n2)

stop

Lezione 5 6

Informatica Industriale

USART Block Diagram

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Lezione 5 7

Informatica Industriale

UART Tx Setup

CSRC Clock Source Selection (synch mode only)1 = Master mode, clock generated by internal BRG

0 = Slave mode, clock derived from external

TX9 9-bit / 8-bit Mode Transmission Selection1 = 9-bit Transmission Format

0 = 8-bit Transmission Format

TXEN Transmit Enable (overridden by SREN/CREN in SYNC mode)1 = Transmitter Enabled

0 = Transmitter Disabled

SYNC Synchronous / Asynchronous Selection1 = Synchronous Mode

0 = Asynchronous Mode

BRGH High / Low Baud Rate Selection

1 = High Speed Baud Rate, FOSC / 16

0 = Low Speed Baud Rate, FOSC / 64

TRMT Transmit Shift Register Status

1 = Transmit Shift Register Empty

0 = Transmit Shift Register Full

TX9D 9th Bit of Transmit Data (valid only in 9-bit mode)Written before TXREG, used for parity or address/data

Lezione 5 8

Informatica Industriale

UART Rx Setup

SPEN Serial Port Enable1 = Serial Port Enabled, Uses RX and TX as serial port pins

0 = Serial Pore Disabled, RX and TX general purpose I/Os

RX9 9-bit / 8-bit Mode Reception Selection1 = 9-bit Reception Format

0 = 8-bit Reception Format

SREN Single Receive Enable (Synchronous Mode Only)1 = Enable a Single Receive

0 = Disable Single Receive, cleared when reception completed

CREN Continuous Receive Enable1 = Enables Receiver; Continuous Reception in Synch mode, overriding SREN

0 = Disables Receiver in Asynchronous Mode, SREN controls Synch mode

ADDEN Address Detect Enable1 = Enables 9-bit Address Detection, Interrupt and load RCREG when bit 9 is ‘1’

0 = Disables Address Detection, all bytes received

FERR Framing Error1 = Framing Error Occurred in this byte, clear by read RCREG + receive next byte

0 = No Framing Error

OERR Overrun Error1 = Overrun Error, cleared by clearing CREN

0 = No Overrun Error

RX9D 9th Bit of Received Data (valid only in 9-bit mode)Read before TXREG, used for parity or address/data

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Lezione 5 9

Informatica Industriale

Baud Rate Generator

Lezione 5 10

Informatica Industriale

Esempio Usart TX

void putchar(value){while (PIR1bits.TXIF == 0);// Wait for empty FIFO

TXREG = value;

}

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Lezione 5 11

Informatica Industriale

MCC18 USART

Lezione 5 12

Informatica Industriale

PIC MSSP MODULE(MASTER SYNCHRONOUS SERIAL PORT)

SPI

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Lezione 5 13

Informatica Industriale

SPI

Lezione 5 14

Informatica Industriale

SPI

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Lezione 5 15

Informatica Industriale

MCC18 SPI

Lezione 5 16

Informatica Industriale

PIC MSSP MODULE(MASTER SYNCHRONOUS SERIAL PORT)

I2C BUSCos’è:

• sistema di comunicazione che utilizza solo 2 linee bidirezionali (SDA, SCL): BUS

• permette il collegamento di molti dispositivi sulla stessa linea sia master che slave

a differenza del protocollo RS232 (point 2 point)

• l’aggiunta/rimozione di dispositivi non pregiudica il funzionamento

del sistema già esistente

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Lezione 5 17

Informatica Industriale

I2C BUS

Lezione 5 18

Informatica Industriale

I2C BUS5.0 BIT TRANSFER

Due to the variety of different technology devices

(CMOS, NMOS,bipolar) which can be connected to the

I2C-bus, the levels of the logical ‘0’ (LOW) and ‘1’

(HIGH) are not fixed and depend on the

associated level of VDD (see Section 15.0 for Electrical

Specifications). One clock pulse is generated for each

data bit transferred.

5.1 Data validity

The data on the SDA line must be stable during the

HIGH period of the clock. The HIGH or LOW state of

the data line can only change when the clock signal on

the SCL line is LOW (see Figure 5).

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Lezione 5 19

Informatica Industriale

I2C BUS

5.2 START and STOP conditions

Within the procedure of the I2C-bus, unique situations arise which

are defined as START and STOP conditions (see Figure 6).

A HIGH to LOW transition on the SDA line while SCL is HIGH is one

such unique case. This situation indicates a START condition.

A LOW to HIGH transition on the SDA line while SCL is HIGH

defines a STOP condition.

START and STOP conditions are always generated by the master.

The bus is considered to be busy after the START condition. The

bus is considered to be free again a certain time after the STOP

condition. This bus free situation is specified in Section 15.0.

Detection of START and STOP conditions by devices connected to

the bus is easy if they incorporate the necessary interfacing

hardware. However, microcontrollers with no such interface have to

sample the SDA line at least twice per clock period in order to sense

the transition.

Lezione 5 20

Informatica Industriale

I2C BUS6.2 Acknowledge

Data transfer with acknowledge is obligatory. The

acknowledge-related clock pulse is generated by the

master. The transmitter releases the SDA line (HIGH)

during the acknowledge clock pulse.

The receiver must pull down the SDA line during the

acknowledge clock pulse so that it remains stable LOW

during the HIGH period of this clock pulse .

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Lezione 5 21

Informatica Industriale

PIC I2C BUS

Lezione 5 22

Informatica Industriale

PIC I2C BUS

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Lezione 5 23

Informatica Industriale

MCC18 I2C BUS

I2C EEPROM