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Microprocessors 2lesson 7

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Subjects lesson 7

Planning Interrupts Serial communication /USART Questions

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Interrupt sources

• External Interrupt RA2/INT • TMR0 Overflow Interrupt • PORTA Change Interrupts • 2 Comparator Interrupts • A/D Interrupt • Timer1 Overflow Interrupt • Timer2 Match Interrupt • EEPROM Data Write Interrupt • Fail-Safe Clock Monitor Interrupt • Enhanced CCP Interrupt

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Interrupt Logic

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Program memory map

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Interrupt Software#include "int16CXX.H"

#pragma origin 4

interrupt int_server( void)

{

int16 var;

int_save_registers

// W, STATUS (and PCLATH)

if (T0IF) { /* TMR0 overflow interrupt */

TMR0 = -255;

CharToLed(var);

var=var*2; if (var>=255) var=1;

T0IF = 0; /* reset flag */

int_restore_registers // W, STATUS (and PCLATH)

}

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Main program interrupts

void main( void)

{

while (1)

{

}

}

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Serial CommunicationIntoduction

Morse code telegraphy RS-232 (low-speed, implemented by Serial Ports) RS485 Universal Serial Bus (moderate-speed, for connecting

computers to peripherals) FireWire Fibre Channel (high-speed, for connecting computers

to mass storage devices) InfiniBand (very high speed, broadly comparable in

scope to PCI) Serial Attached SCSI Serial ATA PCI Express

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RS232-C 1

Half duplex Full duplex 5,6,7,8 databits ASCII (0-127) Stop bit(s) Parity DCE (Data communication equipment) DTE(Data terminal Equipment (PC))

Serial Communication

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RS232DB9-connector

9 Pin Connector on a DTE device (PC connection)

Male RS232 DB9

Pin Number Direction of signal:

1 Carrier Detect (CD) (from DCE) Incoming signal from a modem

2 Received Data (RD) Incoming Data from a DCE

3 Transmitted Data (TD) Outgoing Data to a DCE

4 Data Terminal Ready (DTR) Outgoing handshaking signal

5 Signal Ground Common reference voltage

6 Data Set Ready (DSR) Incoming handshaking signal

7 Request To Send (RTS) Outgoing flow control signal

8 Clear To Send (CTS) Incoming flow control signal

9 Ring Indicator (RI) (from DCE) Incoming signal from a modem

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RS232SynchroneA-Synchrone

Synchrone: Always dataflow of bits to

synchronisize A-Synchrone; When no data needed to send no

dataflow. Synchronysation by start and stop bits (So slower)

Serial Communication

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RS232Voltages

RS232

Level Transmitter (V)

Receiver (V)

Space status (0) +5 ... +15 +3 ... +25

Mark status (1) -5 ... -15 -3 ... -25

Not defined - -3 .. -3 …+3 . +3

Serial Communication

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Cabellenght versus baudrate

Baud rate Maximum cabellength(m)

19200 15

9600 150

4800 300

2400 900

RS232 kabellengte volgens Texas Instruments

Serial Communication

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Serial communication

PIC16F688

• Asynchronous

- Auto-wake-up

- Auto baud calibration

- 13-bit Break character

• Synchronous –

selectable clock

• Synchronous –

clock polarity

Serial Communication

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Transmit status+control register

bit 7 CSRC: Clock Source Select bit

Asynchronous mode:

Don’t care

Synchronous mode:

1 = Master mode (clock generated internally from BRG)

0 = Slave mode (clock from external source)

bit 6 TX9: 9-bit Transmit Enable bit

1 = Selects 9-bit transmission

0 = Selects 8-bit transmission

bit 5 TXEN: Transmit Enable bit

1 = Transmit enabled

0 = Transmit disabled

Note: SREN/CREN overrides TXEN in Sync mode.

bit 4 SYNC: USART Mode Select bit

1 = Synchronous mode

0 = Asynchronous mode

bit 3 SENDB: Send Break Character bit

Asynchronous mode:

1 = Send Sync Break on next transmission (cleared by hardware upon completion)

0 = Sync Break transmission completed

Synchronous mode:

Don’t care

bit 2 BRGH: High Baud Rate Select bit

Asynchronous mode:

1 = High speed

0 = Low speed

Synchronous mode:

Unused in this mode

bit 1 TRMT: Transmit Shift Register Status bit

1 = TSR empty

0 = TSR full

bit 0 TX9D: 9th bit of Transmit Data

Can be address/data bit or a parity bit.

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Buad ratecontrol

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Baud ratecalculating

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SETUPfor serialcommunication

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Exercise

In the last week of this quarter you have to finish a programm what shows the working of the serial port. You can do this with 2 persons.

The programm on the 2 boards has to send the measured value from AN0 analogue input to the other board. The value received from the other board has to be shown , binary, on the 8 leds

Serial Communication