1. Input / Output (Peripheral) Interfacing

2. Peripheral devices Peripheral devices
Input devices such as keyboard, switches, Mouse, Microphone
Output devices such as LED, LCD, Monitor, Printer, Speaker

3. Peripheral devices vs. Memory
like a memory chip, it is mapped to a certain location (called the port address)
unlike a memory chip, a peripheral is usually mapped to a single location

4. Peripheral devices vs. Memory (continue)
like a memory chip, you can write to an output device
You can write to a memory chip using the command such as mov [2000], al
You can write to an output device using the OUT command

5. Peripheral devices vs. Memory (continue)
like a memory chip, you can read from an input device
You can read from a memory chip using the command such as mov al, [4000]
You can read from an input device using the IN command

6. Two formats for IN / OUT Instruction
Format 1: 8 bit address
IN AL, port#
example: IN AL, 40H Or
OUT port#, AL
example: OUT E3H, AL
Can address up to 256 I/O devices
I/O MAP
00 H
01 H
FF H

7. Two formats for IN / OUT Instruction
Format 2: 16 bit address
MOV DX, port# IN AL, DX
Example:
MOV DX, 2500H
IN AL, DX Or
MOV DX, port# OUT DX, AL
MOV DX, FF00H
OUT DX, AL
Can address up to 64k I/O devices
I/O MAP
0000 H
0001 H
FFFF H

8. Processor Timing Diagram for any I/O write (OUT instruction) machine cycle

9. Creating a Simple Output Device (16 bit address format)
Use 8-LED’s as output device
Assign an address for this output device for example F000H
Use a Latch and an address decoder such that the LED’s will only respond to the command out with a specific address (let’s assume that the address is F000) and latch the data

10. Use of 74LS373 and Address Decoder: A0
74LS373 Q0 Q1 Q2 Q3 Q4 Q5 Q6 Q7 D0 D1 D2 D3 D4 D5 D6 D7 OE LE :
mov al, 55
mov dx, F000
out dx, al D7 D6 D5 D4 D3 D2
8088 D1
Minimum D0
Mode
IOR
IOW
Address Decoder A A A A A A A A A A A A A A A A
IOW 1 1 1 1 1 1 9 8 7 6 5 4 3 2 1 5 4 3 2 1

11. Processor Timing Diagram for any I/O read (IN instruction) machine cycle

12. Creating a Simple Input Device
Use 8-Switches (keys)
Assign an address for this input device for example F000H
Use 8 bit tri state gate (74244) and an address decoder such that the keys will be read only with the command IN at a specific address (let’s assume that the address is F000)

13. Use of 74LS245 and Address Decoder5V
A18
74LS244 B0 B1 B2 B3 B4 B5 B6 B7 A0 A1 A2 A3 A4 A5 A6 A7 E : A0 D7 :
mov dx, F000
in al, dx D6 D5 D4 D3 D2
8088 D1
Minimum D0
Mode
IOR
IOW
Address Decoder
Same address for input and output? A A A A A A A A A A A A A A A A
IOR 1 1 1 1 1 1 9 8 7 6 5 4 3 2 1 5 4 3 2 1

14. Output Port Design (8 bit address format)
We assign output port address as 99H ( B )

15. Input Port Design (8 bit address format)
We assign input port address as 5FH ( B )

16. تمرین: (چراغ راهنمایی) سه LED سبز، قرمز و زرد از طریق یک لچ 74373 به cpu اینترفیس
شده است برنامه ای به زبان اسمبلی 8088 بنویسید که به ترتیب LED سبز 70 ثانیه LED زرد 4 ثانیه
و LED قرمز 50 ثانیه روشن شده و این کار تکرار شود. فرکانس کلاک اعمالی به CPU را 8MHZ
در نظر بگیرید. آدرس پرت خروجی را 5EH فرض نمایید.

17. 8255: Programmable Peripheral Interface (PPI)

18. 8255 Features One of the most widely used I/O chips
Is a 40-pin DIP chip
Has three separately accessible ports, A, B, and C
which can be programmed as input or output
Has the capabilities of and together

19. 8255 block diagram

20. 8255 Pin description
Port A (PA0-PA7): This 8-bit port A can be programmed all as
input or all as output
PB(PB0-PB7): This 8-bit port B can be programmed all as
PC(PC0-PC7): This 8-bit port C can be all input or all output.
It can also be split into two parts, CU (upper bits PC4-PC7)
and CL (lower bits PC0-PC3). Each can be used for input or
output. Any of PC0 to PC7 can be programmed individually.
RD’ and WR’: (inputs) IOR and IOW of the system bus are
connected to these two pins.

21. 8255 Pin description (cont.)
RESET:(input) used to clear control register. When RESET
is activated, all ports are initialized as input ports. This pin must be connected to the RESET output of the system bus.
A0, A1 and CS’(chip select): While CS selects the entire chip, address pins A0 and A1 select the specific port within the These three pins are used to access ports A, B, C, and the control register, as shown in Table 11-3.
D0-D7: Data bus of chip which are connected to CPU data bus.

22. 8255 Pin description (cont.)

23. Mode selection of the 8255
While ports A, B and C are used for I/O data, it is the control register that must be programmed to select the operation mode of the three ports A, B and C.

24. The modes of 8255 ports
Mode 0, simple I/O mode. In this mode, any of the ports A, B, CL and CU can be programmed as input or output. In this mode, all bits are out or all are in. In other words, there is no control of individual bits.
Mode 1. In this mode, ports A and B can be used as input or output ports with handshaking capabilities.
Mode 2. In this mode, port A can be used as a bidirectional I/O port with handshaking capabilities.

25. Programming of 8255
The 8255 is programmed in any of the mode by sending a byte (Intel calls it control word) to the control register of the 8255 (as shown in fig )

26. Example: Mode 0

27. Example: Mode 0 (cont.)

28. BSR(Bit Set Rest) mode
In BSR mode, we can set or reset bits of port C individually
We can do it by writing a proper control word in control register (as shown in fig 5 )

29. Example for BSR Program 8255 for the following Solution A) B)
A) set PC2 to high
B) Use PC6 to generate a square wave of 66% duty cycle
Solution A)
MOV AL, B OUT 93H,AL B)
AGAIN MOV AL, 0xxx OUT 93H, AL CALL Delay CALL Delay MOV AL, 0xxx OUT 93H, AL CALL Delay JMP AGAIN

30. Dac adc