1. AVR ATMega32 Elementary Input / Output
Module 9
AVR ATMega32 Elementary Input / Output

2. ATMega32 Input / Output
One of the basic and essential features designed in a computer system is its ability to exchange data with other external devices, and to allow the user to interact with the system:
Input Devices include:
Switches, Keyboards, Mice, Scanners, Cameras, etc.
Output devices include:
Lamp/LED/LCD displays, Video monitors, Speakers, Printers, etc.
One or more interface circuits usually are used between I/O devices and the CPU to:
Handle transfer of data between CPU and I/O interface.
Handle transfer of data between I/O device and interface.
Enable the CPU to request the status of data sent/received by the interface.
Common I/O interfaces:
Elementary I/O: Simple two-state devices such as LED and switches
Parallel I/O: Date exchanged one byte at a time.
Serial I/O: Data exchanged one bit at a time. I

3. Microprocessor I/O Interfacing
Most I/O requests are made by applications or the operating system, and involve moving data between a peripheral device and main memory.
There are three main ways that programs communicate with devices.
I/O Addressing
Direct Access Memory
Interrupts I

4. Microprocessor I/O Interfacing
Port-Based (Standard I/O-Direct I/O)
I/O addresses are seperated from memory addresses
Processor’s software reads and writes a port just like a register
E.g., PA0 = 0xFF
Advantages: Do not take memory addressing space
Disadvatage: Use only IN or OUT instrcutions to transfer data
Memory-Mapped I/O
I/O ports treated as memory locations
Advantages: Accessing I/O ports is like accessing memory loactions
Disadvantages: Take memory addressing space I

5. ATMega32 I/O Ports
The pins marked ‘Gnd’ are to be grounded, ‘Vcc & AVcc’ are to be given 5V.  The Reset pin is also high but we usually prefer to put a switch at this point for the reset of the chips. If the switch is pressed for a minimum pulse of time then it will Reset the chip.
Note: ‘AVcc’ should be connected to 5V supply through a capacitor when using PORTA pins as ADC, though in simple applications capacitor is not necessary. I

6. ATMega32 I/O Port Registers
There are three registers associated with Input/ Output Ports in AVR. I

7. ATMega32 I/O Port Registers
Selecting the direction of pin:-  
DDRxn bit (in the DDRx Register) selects the direction of this pin. 
DDRxn =1, Portx nth pin is configured as an output pin (since there are eight pins in all in a particular port so ‘n’ can be any number between 0-7). 
DDRxn=0, Portx nth is configured as an input pin.
Activating the pull resistors:-
PORTxn= 1, the pull up resistors are activated (while the nth pin is configured as input pin)
PORTxn= 0, the pull up resistors are deactivated (for nth pin).
Inputs of the AVR are generally in Hi-Z state. This makes them prone to catching noise and picking up false signals. So it is advisable to activate the pull up resistor to reduce noise I

8. ATMega32 I/O Port Registers
Status of pin when configured as an output pin:- 
PORTxn= 1, portx nth pin is driven high (one)
PORTxn= 0, portx nth pin is driven low (zero)
PINx Register:-
To put it bluntly, the PINx register contains the status of all the pins in that port. 
If the pin is an input pin, then its corresponding bit will mimic the logic level given to it. 
If it is an output pin, its bit will contain the data that has been previously output on that pin. (The value of an output pin is latched to PINxn bit, you can observe it when we do step by step execution in AVR-Studio shown below) I

9. ATMega32 I/O Pull UP/DOWN Resistors
Pull up resistors are used to pull logic signals up (to logic 1). So when some input signal needs to be set to logic 1, but might need to be changed for some reason to 0 at some other time, a pull-up resistor can keep the signal at logic 1 until the signal is pulled down by something. Typical application for pull up resistors is to connect 4.7 k-ohm (or some other suitable resistor value usually between 1 k-ohm and 10 k-ohm) from the circuit operating voltage (+5V usually) to the input pin. This resistor keep the signal at logic 1. When the signal needs to be set to 0 it is pulled down by connecting that input pin to ground (usually through a button, DIP switch or open collector output of some other part of circuit).
Pull-down resistors work in the opposite way. They keep signal a logic 0 until something connect to signal input to +5V (or whatever the operating voltage of the logic circuit is). I

10. ATMega32 I/O Pull UP Resistor

11. ATMega32 I/O Port: Example 1
The AVR assembly code below shows how to configure the pins on portA of an AVR ATMega32 microcontroller.
.include "m32def.inc"
LDI R16, 0xFF ; Load 0b in R16
OUT DDRA, R ; Configure PortA as an Output port
LDI R16, 0x ; Load 0b in R16
OUT DDRB, R ; Configure PortB as an Input port
LDI R16, 0xF ; Load 0b in R16
OUT DDRC, R ; Configure first four pins on PortC
; as input and the others as output I

12. ATMega32 I/O Port: Example 2
The following code will toggle all 8 bits of Port B forever with some time delay between “on” and “off” states:
LDI R16,0xFF ;R16 = 0xFF = 0b
OUT DDRB,R16 ;make Port B an output port ( )
L1: LDI R16,0x55 ;R16 = 0x55 = 0b
OUT PORTB,R16 ;put 0x55 on port B pins
CALL DELAY
LDI R16,0xAA ;R16 = 0xAA = 0b
OUT PORTB,R16 ;put 0xAA on port B pins
RJMP L1 I

13. ATMega32 I/O Port: Example 3
The following code gets the data present at the pins of port C and sends it to port B indefinitely, after adding the value 5 to it:
.INCLUDE "M32DEF.INC"
LDI R16,0x00 ;R16 = (binary)
OUT DDRC,R16 ;make Port C an input port
LDI R16,0xFF ;R16 = (binary)
OUT DDRB,R16 ;make Port B an output port(1 for Out)
L2: IN R16,PINC ;read data from Port C and put in R16
LDI R17,5
ADD R16,R17 ;add 5 to it
OUT PORTB,R16 ;send it to Port B
RJMP L2 ;continue forever I

14. ATMega32 I/O Port: SBI & CBI Instructions
SBI (Set Bit in IO register)
SBI ioReg, bit ;ioReg.bit = 1
Examples:
SBI PORTD,0 ;PORTD.0 = 1
SBI DDRC,5 ;DDRC.5 = 1
CBI (Clear Bit in IO register)
CBI ioReg, bit ;ioReg.bit = 0
CBI PORTD,0 ;PORTD.0 = 0
CBI DDRC,5 ;DDRC.5 = 0 I

15. ATMega32 I/O Port: Example 4
Write a program that toggles PORTA.4 continuously.
.INCLUDE “M32DEF.INC”
SBI DDRA,4
L1: SBI PORTA,4
CBI PORTA,4
RJMP L1 I

16. ATMega32 I/O Port: SBIC & SBIS Instructions
SBIC (Skip if Bit in IO register Cleared)
SBIC ioReg, bit ; if (ioReg.bit = 0) skip next instruction
Example:
SBIC PORTD,0 ;skip next instruction if PORTD.0=0
INC R20
LDI R19,0x23
SBIS (Skip if Bit in IO register Set)
SBIS ioReg, bit ; if (ioReg.bit = 1) skip next instruction
SBIS PORTD,0 ;skip next instruction if PORTD.0=1 I

17. ATMega32 I/O Port: Example 5
Write a program to perform the following:
(a) Keep monitoring the PB2 bit until it becomes HIGH;
(b) When PB2 becomes HIGH, write value $45 to Port C, and also send a HIGH-to-LOW pulse to PD3.
.INCLUDE "M32DEF.INC"
CBI DDRB, 2 ;make PB2 an input
SBI PORTB,2
LDI R16, 0xFF
OUT DDRC, R16 ;make Port C an output port
SBI DDRD, 3 ;make PD3 an output
AGAIN: SBIS PINB, 2 ;Skip if Bit PB2 is HIGH
RJMP AGAIN ;keep checking if LOW
LDI R16, 0x45
OUT PORTC, R16 ;write 0x45 to port C
SBI PORTD, 3 ;set bit PD3 (H-to-L)
CBI PORTD, 3 ;clear bit PD3
HERE: RJMP HERE I

18. ATmega32 Elementary I/O I

19. ATMega32 Elementary I/O Two-state peripheral devices
May involve more than one bit - e.g., BCD
Requirements
Bit signals can be written to output devices under program control
Bit signals can be read from input devices under program control
Devices required
Latches such as 74LS374 for output
Tri-state buffers such as 74LS244 for input
Example Output devices
LED, bulbs
Relay coils
7-segment display
Example Input devices
Push button
Proximity switch
Rotary BCD coder I

20. ATMega32 Elementary I/O: LEDs
An LED is a semiconductor device that converts electrical energy directly into a discrete color of light
LEDs must be connected the correct way round, the diagram may be labeled a or + for anode and k or - for cathode (yes, it really is k, not c, for cathode!). The cathode is the short lead and there may be a slight flat on the body of round LEDs. If you can see inside the LED the cathode is the larger electrode (but this is not an official identification method).
LEDs can be damaged by heat when soldering, but the risk is small unless you are very slow. No special precautions are needed for soldering most LEDs.
LEDs are available in red, orange, amber, yellow, green, blue and white. Blue and white LEDs are much more expensive than the other colors. The color of an LED is determined by the semiconductor material, not by the coloring of the 'package' (the plastic body). I

21. ATMega32 Elementary I/O: LEDs
Never connect an LED directly to a battery or power supply! It will be destroyed almost instantly because too much current will pass through and burn it out.
LEDs must have a resistor in series to limit the current to a safe value, for quick testing purposes a 1k resistor is suitable for most LEDs if your supply voltage is 12V or less.
The resistor value, R is given by:
Estimate V voltage drop (VL)
Typically draws mA (I)
Unless you know what are you doing! I

22. ATMega32 Elementary I/O: LEDs
Turning on an LED
+5V R
output pin 1
+3.2V
No current
Current
light
Estimate R =
voltage
current =
5 – 1.8 – 0.4
13 x 10 -3
= 215 Ω ~ 220 Ω
easier to get
LED
no light
+0.4V
Setting the pin to high will not turn ON the LED
Voltage drop through an LED is normally between 1.5V to 2.2V. For this problem, it is assumed the voltage drop is 1.8V. Hence, the voltage after the LED is 3.2V. And the calculation is as presented.
Setting the pin to low will turn ON the LED I

23. ATMega32 Elementary I/O: LEDs

24. ATMega32 Elementary I/O: LEDs

25. ATMega32 Elementary I/O: LEDs
.include "M32def.inc"
.ORG 0
LDI R20,high(RAMEND)
OUT SPH, R20
LDI R20,low(RAMEND)
OUT SPL, R20
LDI R20,0xFF ;Set Port A as output
OUT DDRA, R20
LDI R20, 0x00 ;r0 <-- 0
loop:
INC R20 ;r0 <-- r0+1
OUT PORTA, R20 ;Port A <-R20
CALL delay1s ;delay
RJMP loop
delay1s:
LDI R16,200
delay1s0:
LDI R17,0xFF
delay1s1:
DEC R17
BRNE delay1s1
DEC R16
BRNE delay1s0
RET I

26. ATMega32 Elementary I/O: 7-Segment Display
There are applications where you need to display a decimal digit using a seven segment LED display.
The display could represent e.g. the number of times a switch was pressed.
Digits 0-9 and hex A-F can be displayed by giving the proper 7-segment codes q g f e d c b a 1 8 9 2 A 3 4 C 5 6 E 7 F I

27. ATMega32 Elementary I/O: 7-Segment Display
Common-anode :
requires VCC
LED ON when Output is LOW.
Common-cathode :
NO VCC ,
LED ON when Output is HIGH.
TTL and CMOS devices are normally not used to drive the common-cathode display directly because of current (mA) requirement. A buffer circuit is used between the decoder chips and common-cathode display I

28. ATMega32 Elementary I/O: 7-Segment Display

29. ATMega32 Elementary I/O: 7-Segment Display
A 7-Segment LED could be attached as shown: I

30. ATMega32 Elementary I/O: 7-Segment Display
Or: I

31. ATMega32 I/O Port: Example 6
A 7-segment is connected to PORTA. Display 1 on the 7-segment.
DDRC:
PORTC:
.INCLUDE “M32DEF.INC”
LDI R20,0x06 ;R20 = (binary)
OUT PORTC,R20 ;PORTC = R20
LDI R20,0xFF ;R20 = (binary)
OUT DDRC,R20 ;DDRC = R20 ;Delay 1
;cycle latency
L1: RJMP L1
ATmega32 5 1 8 6
PORTC 4 2 3 I

32. ATMega32 I/O Port: Example 7

33. ATMega32 I/O Port: Example 8

34. EXAMPLE 9 7SEGMENT USING ARRAY
Using the 7Segment connected in slide 29 or 30, write a program to display from 0 to 9 continuously.
.INCLUDE “M32DEF.INC”
LDI R16,$FF ;initialize
OUT DDRB,R16
SEMULA: LDI R31, HIGH (CORAK<<1) ;or use ZH
LDI R30, LOW(CORAK<<1) ;or use ZL
LDI R17,#10
ULANG: LPM R18,Z
OUT PORTB,R18
INC ZL
DEC R17
BRNE ULANG
RJMP SEMULA
CORAK: .DB $3F, $06, $5B, $4F, $66, $6D, $7D, $03, $7F, $6F II

35. ATMega32 I/O Problems? I/O’s are SCARCE
Not enough time to buy µC with more I/O’s
Required model not readily available
Compatibility issues esp. using assembly language
Or simply no budget
Solution?
Use MSI Devices I

36. MSI Devices Both Input and Output
MUST read the datasheet for logic details
Input
Buffer: 74LS541
PISO: 74LS165
Priority Encoder: 74LS148 (in tutorial only)
Output
Latch: level trigger: 74LS373
Latch: edge trigger: 74LS574
SIPO: 74LS195
Both Input and Output
Bi-directional buffer: 74LS245
Keypad Encoder: MM74C922 I

37. MSI Devices - Buffer
Isolate shared data bus especially for input into µC
Only one control pin, the rest for data: total 9 pins
GND
PIN_0 I

38. MSI Devices - PISO Parallel Input Serial Output, 74LS165
To save number of input pins into µC
Two control pins, one data input into µC: total 3 pins
PIN_2
VCC/Gnd
PIN_0
PIN_1 I

39. MSI Devices – Priority Encoder
To select the most important input first
Opps… can only learn using Mr. Zulfakar Wise AVR board and attend the tutorial
Indigenous solution to replace expensive 74HC922 (RM6 compared to RM24) I

40. MSI Devices – Example 10 - Inputs
Increase number of input pins of µC: twice of ports
Port_B, PIN_7
Port_B, PIN_0
Port_B, PIN_7
Port_B, PIN_0
VCC
VCC
Buffer 0
Buffer 1
Gnd
Gnd
Port_C, PIN_0 (enable)
Port_C, PIN_1 (enable)
Can be replaced with push buttons etc. I

41. MSI Devices – Example 10 - Inputs
CBI PORTC,0 ;PORTC.0 = 0 (enable)
SBI DDRC,5 ;DDRC.5 = 1 (output)
IN R16, PORTB
SBI PORTC,0 ;PORTC.0 = 1 (disable)
CBI PORTC,1 ;PORTC.0 = 0 (enable)
IN R17, PORTB
SBI PORTC,1 ;PORTC.1 = 1 (disable)
Enable Buffer 0
Read Buffer 0
Store Buffer 0
Enable Buffer 1
Read Buffer 1
Store Buffer 1

42. MSI Devices – Latch level Trigger
To store data by level trigger
Increase output pins, min. one control pin
Output enable for bus sharing
Latch: level trigger: 74LS373 I

43. MSI Devices – Latch Edge Trigger
To store data by edge trigger
Increase output pins, min. one control pin
Output enable for bus sharing
Latch: edge trigger: 74LS574 compatible with
74LS374 but different pins arrangement
PIN_0 (clk)
PIN_1 (enable) I

44. MSI Devices - SIPO Serial Input Parallel Output 74LS195
Gnd
PIN_0 (CLK)
VCC
PIN_1 (data out)
Serial Input Parallel Output
74LS195
To store data by edge trigger
Increase output pins from µC:
use only two pins I

45. MSI Devices – Example 11 - Outputs
Increase number of input pins of µC: twice of ports
Port_B, PIN_0
Port_B, PIN_7
Port_B, PIN_0
Port_B, PIN_7
Port_C, PIN_2 (clk)
Port_C, PIN_3 (clk)
Latch 0
Latch 1
Gnd
Gnd
Gnd
No bus sharing, output can always enable I

46. MSI Devices – Example 11 - Outputs
LDI R18, 0xFF
LD DDRB, R18
LDI R19, 0x89 ;Prepare data LED
OUT PORTB, R19 ;
CBI PORTC,2 ;PORTC.2 = 0 (enable)
SBI DDRC,2 ;DDRC.2 = 1 (output)
SBI PORTC,2 ;PORTC.2 = 1 (disable)
LDI R20, 0xC3 ;Prepare data 7Segment
OUT PORTB, R20 ;
CBI PORTC,3 ;PORTC.3 = 0 (enable)
SBI DDRC,3 ;DDRC.3 = 1 (output)
SBI PORTC,3 ;PORTC.3 = 1 (disable)
Prepare LED
Send to LED
Prepare 7Seg
Send to 7Seg
What is the pattern of the 7Segment?

47. MSI Devices – Bi-directional Buffer
Can either be both Input or Output
To control shared data bus
Bi-directional buffer: 74LS245
PIN_1 (enable)
PIN_0 (direction) I

48. MSI Devices – Keypad Encoder
MM74C922
Have both Input (push buttons) and Output (into µC): total 6 pins
Use to read keypads
interrupt
PIN_0
PIN_1 (enable) I

49. MSI Devices – Keypad Encoder Truth Table
0 to 15 for MM74C922
0 to 19 for MM74C923 I

50. MSI Devices – Example Keypads
Interrupt to PortC, Pin 4
Enable PortC, Pin 5
Data connected to PortB, pin 0 to 3
Upon interrupt pin 4 call, do:
CBI PORTC,5 ;PORTC.5 = 0 (enable)
SBI DDRC,5 ;DDRC.5 = 1 (output)
IN R21, PortB
SBI PORTC,5 ;PORTC.5 = 1 (disable)
LDI R22, 0x0F
AND R21,R22 ; filter unwanted data pin B4 to B7 I

51. ASSIGNMENT Enter 4 keys using keypads: Display every entry at 7Segment
Press ‘#’ as enter key or end of entry
If password is correct, display pass 7Segment and turn off all red LED
If password is wrong, display fail at 7Segment and blink 1 red LED I