1st Seminar 12 09 12 BIOS Serial Xmission

7/30/2019 1st Seminar 12 09 12 BIOS Serial Xmission

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27 November 2012 1

PRESENTED BY

MITUL MODI(ME MSA 199)

M S UNIVERSITY, BARODA

2012-13

BIOS Serial Data Transmission INT Services

and

Serial Modem Port Control


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Data Transmission Technology

Data transmission technologies are used to connect two devices directly.

These technologies used to provide a physical connection that can be used to

carry many higher level programming

Beside a network card, PARALLEL AND SERIAL PORT provide a way to get

data IN and OUT of microprocessor.

Parallel Port:

1. Transfer 8 bit data at a time.

2. Most common use is to drive printer.

3. LPT1, LPT2,LPT3 : Logical Designators

4. 25 pin D Connector.

Serial Port:

1. Transfer one bit at a time.2. Most common is to connect Modem.

3. COM1, COM2, COM3, COM4 : Logical Designator.

4. 9 pin D Connector.

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Steps for Data Transmission:

When program wants to send something (data) out through port it

1. First load data in data segment register of microprocessor.

2. Initialized serial port.

3. Load necessary parameter in al register for serial data transmission.

4. Use serial data transmission interrupt (INT 14h) to transmit data to port.

Basic Interrupt Processing

Mechanism which causes the processor to stop execution of current program and

transfer control to ISR handler and resume current execution on completion ofISR.

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Step: 2 Initialization of Serial Port:

Execution of any interrupts using BIOS INT 14h. We have to perform

following assembly instructions.

mov ah,CODE ; code is loaded in AH

mov al, PARAMETER ;

int 14h

Code Description

00h Serial Port Initialization

01h Transmit Character

02h Receiving Character

03h Status

Serial Port for Communication:

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Step:3 Necessary Parameter for Communication:

Parameter

Bit Description

0 Word Size 00= 5 01 = 610 =7 11 =81

2 Stop Bit 0 = 1 stop bit

1 = 2 stop bit

3 Parity 00 = None

01 = Odd11 = Even

4

5 Baud Rate : 000 = 110 baud

001 = 150 baud

010 = 300 baud

011 = 600 baud

100 =1200 baud

101 = 2400 baud

110 = 4800 baud

111 = 9600 baud

6

7

Baud rate: a data transmission rate (bits/second) for modems.27 November 2012 5


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Port Initialization Code : (00h)

Setting parameters for necessary communication like word size, stop bit, parity

and baud rate etc. & load accordingly parameter to AL.

Code (i.e. 00h) is loaded in AH register.

INPUT OUTPUT

AX 00h Parameter AX RS232 Status Modem Status

DX Port No. ( 0-3) DX

Port Transmission Code : (01h)

Code (i.e. 01h) is loaded in AH register.

Character is to be transmitted and loaded in AL register.

INPUT OUTPUT

AX 01h Character AX RS232 Status Modem Status

DX Port No. ( 0-3) DX

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There are several many serial transmission standards available for use in

microprocessor including RS232, USB.

Advantages of Serial Bus:

1. Signal Integrity , Less cross talk, lesser noise2. Low cost

Disadvantages of Serial Bus:

1. Higher clock rates require for given bandwidth.

RS232 Interface:

Used for asynchronous serial data transmission.

Nominal Logic Levels : Logic 0 : +12 V Logic 1 : -12 V

allows signals are to be transmitter over greater distance.

specifies maximum cable length 75 feet at 9600 bps.

Common Signals : Pin Desciption

1. Data Carrier Detect : DCD 6. Data Set Ready : DSR2. Receive Data : RD 7. Request To Send : RTS

3. Transmitted Data :TD 8. Clear To Set : CTS

4. Data Terminal Ready : DTR 9. Ring Indicator : RI

5. Signal Ground : GND

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DB 25 Pin Description:

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Modem:

Contraction of modulation and demodulation.

Used to send and receive serial data over telephonic line.

Consists of three basic hardware and software components i.e. data pump, controllerand UART .

Audio signal are also known as carrier signal.

Basics of modems:

RS 232 data terminal equipment (DTE) Modem, data communication

equipment (DCE) telephonic line

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Steps for Data Receiving:

When a character arrives

1. Port places an interrupt message in interrupt request queue.

2. Processor stops what it is doing, save the state of flags and address on stack.

3. Transferring control to interrupt handling program.

4. Interrupt handling program changes processor to I/O addressing mode.

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BIOS Serial Port Status: (AH Reg.)

Bit - 7 Bit - 6 Bit - 5 Bit - 4 Bit - 3 Bit -2 Bit - 1 Bit

0

Time

Out

TSRE THRE Break

Detected

Frame

Error

Parity

Error

Overrun

Error

RDA

Received DataAvailable

Transmit Holding Reg. Empty

Transmit Shift Reg. Empty

Occurs if received char. w/ovalid stop bit


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BIOS Modem Port Status: (AL Reg.)

Bit - 7 Bit - 6 Bit - 5 Bit - 4 Bit - 3 Bit -2 Bit - 1 Bit 0

RLSD RI DSR CTS Change

inRLSD

Trailing

EdgeRI

Change

in DSR

Change

in CTS

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Ring Indicator

Data Set Ready

Clear to Send

Received Line

Signal Detect


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Program Code for transmission of data:

.data

strg1 dw R, E, S, I, S, T, E, R

.code.startup

mov ax, @ data ;

mov ds, ax ;

mov ds, [0000h] ; Select Port 1

mov cx, 08h ; Set count equal to String Length

mov ah, 00h ; Serial port initializemov al, 0e7h ; Parameter set up

int 14h ; BIOS Interrupt

LOOP1: lea si, strg1 ; Load effective add. of string

mov ah, 01h ; Code for Transmission

mov al, [si] ;

int 14h ;inc si ;

loop LOOP1 ;

.end

Segment Initialization

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Program Code for receiving of data:

.data

strg2 dw 10 dup(?)

.code.startup

mov ax, @ data ;

mov ds, ax ;

mov ds, [0000h] ; Select Port 1

mov ah, 00h ; Serial port initialize

mov al, 0e7h ; Parameter set upint 14h ; BIOS Interrupt

mov cx, 08h ; Set count equal to String Length

LOOP1: mov ah, 02h ; Code for Receiver

lea di, strg2 ; Load effective add. of string

int 14h ;

mov [di], al ;inc di ;

loop LOOP2 ;

.end

Segment Initialization

Received character copied to destinationAdd.

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1st Seminar 12 09 12 BIOS Serial Xmission

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