ECE291 Lecture 8 Peripheral devices. ECE 291 Lecture 8Page 2 of 37 Lecture outline Hardware I/O with ports 8253 timer PC speaker Serial port Parallel

ECE291ECE291

Lecture 8Lecture 8

Peripheral devicesPeripheral devices

ECE 291 Lecture 8ECE 291 Lecture 8

Page Page 22 of 37 of 37

Lecture outlineLecture outline

Hardware I/O with portsHardware I/O with ports

8253 timer8253 timer

PC speakerPC speaker

Serial portSerial port

Parallel portParallel port



Port input and outputPort input and output

Used to communicate with many Used to communicate with many peripheral devices built into the processor, peripheral devices built into the processor, motherboard or expansion cardsmotherboard or expansion cards

ININ instruction transfers data from a device instruction transfers data from a device on the I/O bus to AL, AX, or EAXon the I/O bus to AL, AX, or EAX

OUTOUT instruction transfers data from AL, instruction transfers data from AL, AX, or EAX to a device connected to the AX, or EAX to a device connected to the I/O busI/O bus



Port input and outputPort input and output

Two forms of port addressingTwo forms of port addressing

Fixed-port addressingFixed-port addressing Allows an 8-bit I/O port address (use if port is 0 – 255)Allows an 8-bit I/O port address (use if port is 0 – 255) port number is immediate (follows the instruction opcode)port number is immediate (follows the instruction opcode)

IN AL, 6AhIN AL, 6Ah ;data from I/O address 6Ah is input to AL;data from I/O address 6Ah is input to AL

Variable-port addressingVariable-port addressing Allows using 16-bit port address (addresses up to FFFFh)Allows using 16-bit port address (addresses up to FFFFh) the I/O port number is stored in register DXthe I/O port number is stored in register DX

MOV DX, 0FA64hMOV DX, 0FA64h

OUT DX, AX OUT DX, AX ;transfers contents of AX to I/O port FA64h;transfers contents of AX to I/O port FA64h



Port I/O examplePort I/O example..START

IN al, 61h ;read port 61h: PC speaker control register

OR al, 3 ;set bits 0 and 1

OUT 61h, al ;turn speaker on

MOV cx, 1000h ;delay count; if the count is increased,

;the beep will become longer

.L1 LOOP .L1 ;time delay – spin 1000h times

IN al, 61h

AND al, 0fch ;clear bits 0 and 1

OUT 61h, al ;turn speaker off

MOV ax, 4c00h ;Normal DOS Exit

INT 21h



Keyboard controlKeyboard controlThe keyboard is connected to the 8255 Programmable The keyboard is connected to the 8255 Programmable Peripheral Interface (PPI) chip, a simple self-contained Peripheral Interface (PPI) chip, a simple self-contained or embedded microprocessoror embedded microprocessor

Contains three registers A, B, and C which are accessed on Contains three registers A, B, and C which are accessed on ports ports 60h-62h60h-62h using the in/out instructions using the in/out instructions

When a key is pressed or released two events take When a key is pressed or released two events take place:place:

an 8-bit scan code is deposited in an 8-bit scan code is deposited in register Aregister A of the PPI of the PPI

an an INT 09hINT 09h hardware interrupt is generated hardware interrupt is generated

Default ISR gets the scan code in A, acknowledges the hardware Default ISR gets the scan code in A, acknowledges the hardware interrupt, and passes information to the keyboard buffer (a memory interrupt, and passes information to the keyboard buffer (a memory buffer in BIOS data area)buffer in BIOS data area)



Keyboard controlKeyboard control

Each key action is stored in the buffer as a wordEach key action is stored in the buffer as a word normal charactersnormal characters are stored with ASCII code for the character, are stored with ASCII code for the character,

and the scan code for the keyand the scan code for the key extended codesextended codes corresponding to special keys e.g., cursor corresponding to special keys e.g., cursor

keys, shiftkeys, shift

The keyboard buffer is a The keyboard buffer is a circular buffercircular buffer, when it gets full , when it gets full and a new key is pressed:and a new key is pressed:

INT 09 ISR generates a “bell” character, which causes the INT 09 ISR generates a “bell” character, which causes the speaker to beepspeaker to beep

The data from the new key press is discardedThe data from the new key press is discarded

Keyboard buffer holds keystrokes until read by an int 16Keyboard buffer holds keystrokes until read by an int 16



8253 Programmable Timer8253 Programmable TimerIntel 8253 contains 3 independent 16-bit programmable Intel 8253 contains 3 independent 16-bit programmable counterscounters

Operate on a clock frequency of 14.31818 MHzOperate on a clock frequency of 14.31818 MHz

This frequency is divided by 12 before being sent to the This frequency is divided by 12 before being sent to the timer so the pulses arrive at frequency 1.19318 MHztimer so the pulses arrive at frequency 1.19318 MHz

Each timer can be loaded with a sixteen bit starting Each timer can be loaded with a sixteen bit starting count (0 – 65535)count (0 – 65535)

Once enabled, timers repeatedly count down to 0 from Once enabled, timers repeatedly count down to 0 from the starting count and generate an output signalthe starting count and generate an output signal

The rate of the output signal is (1193180 / starting The rate of the output signal is (1193180 / starting count) outputs per secondcount) outputs per second



8253 Programmable Timer8253 Programmable Timer

Timer 0Timer 0 Generates and INT 08h when the timer expires. Can be used to Generates and INT 08h when the timer expires. Can be used to

trigger regularly recurring events in your programs.trigger regularly recurring events in your programs. Counts down from as high as 65535 to zeroCounts down from as high as 65535 to zero The output signal occurs each (1.19318 * 10The output signal occurs each (1.19318 * 1066)/ 65535 = 18.2 Hz)/ 65535 = 18.2 Hz

Timer 1Timer 1 Causes the DRAM memory system to be refreshedCauses the DRAM memory system to be refreshed If you interfere with this function, the entire contents of the If you interfere with this function, the entire contents of the

system memory could be lostsystem memory could be lost

Timer 2Timer 2 General purpose, and optionally connected to the PC speaker General purpose, and optionally connected to the PC speaker

for generating simple tonesfor generating simple tones



Timer control registersTimer control registers

8253 has four byte-sized control registers 8253 has four byte-sized control registers which are mapped to I/O ports 40h-43h which are mapped to I/O ports 40h-43h

PortPort DescriptionDescription

40h 40h Timer 0 Count Register Timer 0 Count Register

41h 41h Timer 1 Count Register Timer 1 Count Register

42h42h Timer 2 Count Register Timer 2 Count Register

43h43h Timer Control RegisterTimer Control Register



TimerTimer

The Control Register allows the programmer to select The Control Register allows the programmer to select the counter, mode of operation, and type of operationthe counter, mode of operation, and type of operation

Bits Bits DescriptionDescription 7,67,6 Counter ID (00,01,10)Counter ID (00,01,10)

5,45,4 00: latch count for reading00: latch count for reading 01: Read/Set least significant byte 01: Read/Set least significant byte 10: Read/Set most significant byte 10: Read/Set most significant byte 11: Read/Set least significant byte then most 11: Read/Set least significant byte then most

significant byte significant byte

3,2,1 3,2,1 Count Mode (011=Square Wave) Count Mode (011=Square Wave) 0 0 Count Method: 0=Binary, 1=BCD Count Method: 0=Binary, 1=BCD



Speaker controlSpeaker control

Timer 2 output from 8253 can be enabled as an analog Timer 2 output from 8253 can be enabled as an analog input to the PC speakerinput to the PC speakerEnable timer input to speaker (port 61h, bit 1) Enable timer input to speaker (port 61h, bit 1) Enable speaker (port 61h, bit 0) Enable speaker (port 61h, bit 0)

Write to Timer Control Port Write to Timer Control Port movmov al,10110110b al,10110110b outout 43h, al43h, al

10:10: Control timer 2 Control timer 2 11:11: Load Low Byte then High Byte Load Low Byte then High Byte

011:011: Select Square wave output Select Square wave output 0:0: Count in binaryCount in binary



Speaker ControlSpeaker Control

Enable Speaker Enable Speaker ININ al, 61hal, 61hOROR al, 00000011bal, 00000011bOUTOUT 61h, al61h, al

Bit 1: Enable Timer Bit 1: Enable Timer

Bit 0: Enable Speaker Bit 0: Enable Speaker

Don't change other bitsDon't change other bits

Write count to timer Write count to timer OUT OUT 42h, al42h, al

MOVMOV al, ah al, ah OUT OUT 42h, al42h, al

AX=count (ticks) = 1193180 (ticks/sec) / Freq (1/sec) AX=count (ticks) = 1193180 (ticks/sec) / Freq (1/sec)



ExampleExampleCR EQU 13LF EQU 10extrn dosxit, kbdin, dspmsg, binasc

; Define stack segmentstkseg SEGMENT stack

RESB 512stktop

; Define code segment cseg SEGMENT CODE; Variable declarationspbuf RESB 7crlf db CR,LF,'$' freq_msg db ' Freq = $' count_msg db ' Hz, Count = $'



Example Example ..start..start

mainmain

mov ax, cs ; Initialize DS registermov ax, cs ; Initialize DS register

mov ds, axmov ds, ax

mov mov al,10110110b al,10110110b ; Timer2, Load L+H, square wave, ; Timer2, Load L+H, square wave, ; binary; binary

out out 43h,al 43h,al ; Write timer control byte ; Write timer control byte

in in al,61h al,61h

or or al,00000011b al,00000011b ; Enable Timer2 & Turn on speaker; Enable Timer2 & Turn on speaker

out out 61h,al61h,al

.mloop.mloop

call call kbdinkbdin

cmp cmp al,'0' al,'0' ; 0 to quit; 0 to quit

je je .mdone.mdone

sub sub al,'0' al,'0'

mov mov ah,0 ah,0



ExampleExamplemov cl,8 ; Freq * 256 (Hz) shl ax,cl

mov dx, freq_msg call dspmsg mov bx, pbuf call binasc mov dx, pbuf call dspmsg ; Print Freq mov bx,ax mov ax,34DCh ;DX:AX=1,193,180 (tics/sec)mov dx,12h ;AX = ----------------------div bx ;BX=Freq (1/sec)mov dx, count_msg call dspmsg mov bx, pbuf call binasc



ExampleExamplemov dx, pbuf

call dspmsg ; Print count

mov dx, crlf

call dspmsg

out 42h,al ; Write Low byte to Timer Channel 2

mov al,ah

out 42h,al ; Write High byte to Timer Channel 2

jmp .mloop

.mdone

in al,61h

and al,11111100b ; Turn off speaker

out 61h,al

call dosxit ; Exit to DOSmain



Serial communicationSerial communication

One of the oldest, simplest, and most widely One of the oldest, simplest, and most widely used forms of communication in the world.used forms of communication in the world. Smoke signalsSmoke signals Morse codeMorse code Early computer miceEarly computer mice Classical mainframe/terminal computingClassical mainframe/terminal computing USB printers, keyboards, scanners, camerasUSB printers, keyboards, scanners, cameras EthernetEthernet The InternetThe Internet Digital cell phonesDigital cell phones Digital satellitesDigital satellites




Can be implemented with as few as two Can be implemented with as few as two (unidirectional) or three (bidirectional) wires(unidirectional) or three (bidirectional) wires Common groundCommon ground Transmit line (Tx)Transmit line (Tx) Receive line (Rx)Receive line (Rx)

One bit transferred at a timeOne bit transferred at a time Takes numerous transfers to move a single byte, but Takes numerous transfers to move a single byte, but

that’s okaythat’s okay Data must be broken down into chunks to transferData must be broken down into chunks to transfer Maybe we want some error checking tooMaybe we want some error checking too




Serial or communications ports are nothing more Serial or communications ports are nothing more than shift registers connected to specific I/O than shift registers connected to specific I/O portsports For transmitting, write data to the port corresponding For transmitting, write data to the port corresponding

to the shift registerto the shift registerShift register moves data out one bit at a time over a serial Shift register moves data out one bit at a time over a serial cablecable

For receiving, the shift register accepts bits as they For receiving, the shift register accepts bits as they come in, shifting them into the register.come in, shifting them into the register.

Read the data from the shift register using the appropriate Read the data from the shift register using the appropriate port addressport address




Start bit indicates when a communication frame Start bit indicates when a communication frame beginsbeginsNext 5-8 bits are the actual data Next 5-8 bits are the actual data Number of data bits is configurableNumber of data bits is configurable 8-bits is very popular because of its obvious 8-bits is very popular because of its obvious

correspondence with the size of a bytecorrespondence with the size of a byte

Start Bit 5-8 Data Bits Parity Bit

Stop Bit(s)




The parity bit indicates if the number of ones The parity bit indicates if the number of ones was even (0) or odd (1). Helpful with error was even (0) or odd (1). Helpful with error checking.checking.Stop bits (1, 1.5 or 2) indicate the end of a data Stop bits (1, 1.5 or 2) indicate the end of a data frameframe

Start Bit 5-8 Data Bits Parity Bit

Stop Bit(s)




Bit or baud rate determines how quickly the bits Bit or baud rate determines how quickly the bits are shifted out of the serial portare shifted out of the serial port Can be as low as 110 bits per secondCan be as low as 110 bits per second Can be as high as 115000 bits per second with Can be as high as 115000 bits per second with

standard serial ports (USB is much faster)standard serial ports (USB is much faster)

Actual rate of data transfer depends port settingsActual rate of data transfer depends port settings 8 data bits, no parity, one stop bit means that 8 of 8 data bits, no parity, one stop bit means that 8 of

every 10 bits that transfer contain useful dataevery 10 bits that transfer contain useful data 5 data bits, parity, 2 stop bits means that only 5 of 5 data bits, parity, 2 stop bits means that only 5 of

every 9 bits contain useful dataevery 9 bits contain useful data




For serial ports to work, both ends must For serial ports to work, both ends must agree on all the previous settingsagree on all the previous settings

Once that’s done, the hardware takes care Once that’s done, the hardware takes care of the messy detailsof the messy details

From the programming side of things, you From the programming side of things, you have to configure the port, then know how have to configure the port, then know how to write data properlyto write data properly




Programming the serial portProgramming the serial port First you should configure the portFirst you should configure the port

Stop bits, data bits, parity, bit rateStop bits, data bits, parity, bit rate To read, check status register until a byte is ready to To read, check status register until a byte is ready to

be read, then read itbe read, then read it To write, check status register until serial port is To write, check status register until serial port is

ready, then write the byteready, then write the byte

This particular paradigm is called pollingThis particular paradigm is called pollingSerial ports also generate hardware interrupts Serial ports also generate hardware interrupts when they receive data, but we won’t be going when they receive data, but we won’t be going that far in MP2that far in MP2



Serial communication - regsSerial communication - regs

For configuring the portFor configuring the port Line control (LCR) – Specifies the data frame (word length, Line control (LCR) – Specifies the data frame (word length,

number of stop bits, and type of parity) for transmitting and number of stop bits, and type of parity) for transmitting and receivingreceiving

Divisor latch low (DLL) – Stores lower 8 bits of the baud-rate Divisor latch low (DLL) – Stores lower 8 bits of the baud-rate generator divisorgenerator divisor

Divisor latch high (DLH) – Stores the upper 8 bits of the baud-Divisor latch high (DLH) – Stores the upper 8 bits of the baud-rate generator divisorrate generator divisor

For transferring dataFor transferring data Line status (LSR) – Contains the transmitter empty, transmit Line status (LSR) – Contains the transmitter empty, transmit

buffer empty, receive buffer full, and receive error flagsbuffer empty, receive buffer full, and receive error flags Receive buffer (RBR) – Holds the byte receivedReceive buffer (RBR) – Holds the byte received Transmit buffer (TBR) – Holds the byte to transmitTransmit buffer (TBR) – Holds the byte to transmit



Serial communication - regsSerial communication - regs

Each serial port has a unique Port I/O address Each serial port has a unique Port I/O address

DeviceDevice Serial port base addressSerial port base address

COM0:COM0: 03F8h 03F8h

COM1:COM1: 02F8h02F8h

COM2:COM2: 03E8h03E8h

COM3:COM3: 02E8h02E8h

The serial port base addresses are stored at 0000:0400 – 0407. You The serial port base addresses are stored at 0000:0400 – 0407. You can view these addresses directly using can view these addresses directly using debugdebug or or td.td.

At the command prompt, type “debug” to get the “-” debug promptAt the command prompt, type “debug” to get the “-” debug prompt type type d0:0400d0:0400 (and hit return) (and hit return)

you get : you get : 0000:04000000:0400 F8 03 F8 02 E8 03 E8 02F8 03 F8 02 E8 03 E8 02 the first four words are addresses of the installed comm portsthe first four words are addresses of the installed comm ports



Register addressesRegister addresses

DLL = Base + 0DLL = Base + 0 Depends on a setting in LCRDepends on a setting in LCR

TBR = Base + 0TBR = Base + 0 Write onlyWrite only

RBR = Base + 0RBR = Base + 0 Read onlyRead only

DLH = Base + 1DLH = Base + 1LCR = Base + 3LCR = Base + 3LSR = Base + 5LSR = Base + 5



Line control registerLine control register

Must set DLAB to Must set DLAB to access DLL and DLHaccess DLL and DLH



Baud rate divisorBaud rate divisorSetting the baud rateSetting the baud rate

Based off 1.8432 MHz Based off 1.8432 MHz clock frequencyclock frequency

Baud rate = frequency / Baud rate = frequency / (16 x divisor)(16 x divisor)

You set the divisor in a You set the divisor in a special control register special control register within the serial portwithin the serial port

Divisor Baud Rate1 1152002 576003 384004 288006 192008 1440012 960024 4800384 300



Line status registerLine status register

Check RBF to see if a Check RBF to see if a byte has been byte has been receivedreceived

Check TE or TBE to Check TE or TBE to see of a byte has see of a byte has been transmittedbeen transmitted



Parallel interfaceParallel interface

Originally designed for use with printers onlyOriginally designed for use with printers only

Provides 8-bit data transfer (originally output only, now bi-Provides 8-bit data transfer (originally output only, now bi-directional)directional)

Provides TTL (5V) external I/OProvides TTL (5V) external I/O

When the computer boots it detects any parallel ports and When the computer boots it detects any parallel ports and assigns ‘logical’ port names to them (LPT1, LPT2, LPT3)assigns ‘logical’ port names to them (LPT1, LPT2, LPT3)

Each parallel port uses three processor I/O portsEach parallel port uses three processor I/O ports datadata output (to send a byte of data to a printer you send the data output (to send a byte of data to a printer you send the data

to the output data register)to the output data register) statusstatus signals from the printer signals from the printer control/commandscontrol/commands to the printer to the printer



Parallel interfaceParallel interface

Each logical device has a unique Port I/O address Each logical device has a unique Port I/O address

DeviceDevice Data PortData Port Status PortStatus Port Control PortControl Port

LPT0:LPT0: 3BCh3BCh 3BDh3BDh 3BEh 3BEh

LPT1:LPT1: 378h378h 379h379h 37Ah 37Ah

LPT2:LPT2: 278h278h 279h279h 27Ah 27Ah

The parallel port base addresses are stored at 40:0008h, and can The parallel port base addresses are stored at 40:0008h, and can be viewed by using be viewed by using debugdebug or or tdtd

At the command prompt, type “debug” to get the “-” debug promptAt the command prompt, type “debug” to get the “-” debug prompt type type d40:0008d40:0008 (and hit return) (and hit return) you get : you get : 0040:00080040:0008 BC 03 78 03 78 02BC 03 78 03 78 02 … … the first six bytes are addresses of the installed printer adaptersthe first six bytes are addresses of the installed printer adapters



Parallel interface major signalsParallel interface major signals

Signal(s)Signal(s) Input/OutputInput/Output NotesNotes

Data[7:0]Data[7:0] Bi-directionalBi-directional Byte-wide data bus Byte-wide data bus

StrobeStrobe To deviceTo device Write signal Write signal

BusyBusy From deviceFrom device Don't send more data Don't send more data

AckAck From deviceFrom device Acknowledge interrupts Acknowledge interrupts

InitializeInitialize To deviceTo device Initialize external device Initialize external device

Out of PaperOut of Paper From deviceFrom device Status signal Status signal



Writing to the parallel interfaceWriting to the parallel interface



Control & Status PortsControl & Status Ports

Control PortControl Port

Bit DescriptionBit Description

7-5 Unused 7-5 Unused

4 IRQ Enable 4 IRQ Enable

3 Select [inverted]3 Select [inverted]

2 Initialize 2 Initialize

1 AutoFeed [inverted]1 AutoFeed [inverted]

0 Strobe [inverted]0 Strobe [inverted]

Status PortStatus Port

Bit DescriptionBit Description

7 Busy [inverted]7 Busy [inverted]

6 Ack 6 Ack

5 Out-of-Paper5 Out-of-Paper

4 Selected4 Selected

3 I/O Error 3 I/O Error

2-0 Unused2-0 Unused

Documents

ECE291 Lecture 8 Peripheral devices. ECE 291 Lecture 8Page 2 of 37 Lecture outline Hardware I/O with ports 8253 timer PC speaker Serial port Parallel