MICROPROCESSORS AND MICROCONTROLLERS
AIM
To have an in depth knowledge of the architecture and programming of 8-bit
and 16-bit Microprocessors, Microcontrollers and to study how to interface
various peripheral devices with them.
OBJECTIVE
To study the architecture and Instruction set of 8085 and 8086
To develop assembly language programs in 8085 and 8086.
To design and understand multiprocessor configurations
To study different peripheral devices and their interfacing to 8085/8086.
To study the architecture and programming of 8051 microcontroller.
UNIT I THE 8085 AND 8086 MICROPROCESSORS
8085 Microprocessor architecture-Addressing modes- Instruction set-Programming the 8085
UNIT II 8086 SOFTWARE ASPECTS
Intel 8086 microprocessor - Architecture - Signals- Instruction Set-Addressing Modes-Assembler Directives- Assembly Language Programming-Procedures-Macros-Interrupts And Interrupt Service Routines-BIOS function calls.
UNIT III MULTIPROCESSOR CONFIGURATIONS Coprocessor Configuration – Closely Coupled Configuration – Loosely Coupled Configuration –8087 Numeric Data Processor – Data Types – Architecture –8089 I/O Processor –Architecture –Communication between CPU and IOP.
UNIT IV I/O INTERFACING Memory interfacing and I/O interfacing with 8085 – parallel communication interface – serial communication interface – timer-keyboard/display controller – interrupt controller – DMA controller (8237) – applications – stepper motor – temperature control.
UNIT V MICROCONTROLLERS Architecture of 8051 Microcontroller – signals – I/O ports – memory – counters and timers – serial data I/O – interrupts-
Interfacing -keyboard, LCD,ADC & DAC
UNIT I
THE 8085 MICROPROCESSOR
1.1 Introduction to 8085
1.2 Microprocessor architecture
1.3 Instruction set
1.4 Addressing modes
1.5 Programming the 8085.
1.1 8085 PROCESSOR
•The first microprocessor was introduced in 1970 by Intel (named 4004).
• It ran at the speed of 108KHz.
• Four years later, Intel created the 8080 running at just over 2 Mhz.
•This microprocessor was used on the world's firs personal computer, named Altair.
•Also at this time, IBM started researching for their microprocessor, called POWER
(Performance Optimization With Enhanced RISC).
1.2 Microprocessor architecture
Control Unit
Arithmetic Logic Unit
Registers
Accumulator
Flags
Program Counter (PC)
Stack Pointer (SP)
Instruction Register/Decoder
Memory Address Register
General Purpose Registers
Control Generator
Register Selector
Microprogramming
8085 ARCHITECTURE
CONTD..
1.3 INSTRUCTION SET
BASED ON FUNCTIONS
Data Transfer Instructions
Arithmetic Instructions
Logical Instructions
Branch Instructions
Machine Control
BASED ON LENGTH
One-word or 1-byte instructions
Two-word or 2-byte instructions
Three-word or 3-byte instructions
8085 Instruction Set
The 8085 instructions can be classified as follows:
Data transfer operations
Between Registers
Between Memory location and a Registers
Direct write to a Register/Memory
Between I/O device and Accumulator
Arithmetic operations (ADD, SUB, INR, DCR)
Logic operations
Branching operations (JMP, CALL, RET)
8085 Instruction Types
8085 Instruction Types
8085 Instruction Types
PIN DIAGRAM
1.5 ADDRESSING MODES
Implied Addressing:
The addressing mode of certain instructions is implied by the instruction’s function.
For example, the STC (set carry flag) instruction deals only with the carry flag, the
DAA (decimal adjust accumulator) instruction deals with the accumulator.
Register Addressing:
Quite a large set of instructions call for register addressing. With these instructions,
specify one of the registers A through E, H or L as well as the operation code. With
these instructions, the accumulator is implied as a second operand. For example,
the instruction CMP E may be interpreted as 'compare the contents of the E register
with the contents of the accumulator.
Most of the instructions that use register addressing deal with 8-bit values.
However, a few of these instructions deal with 16-bit register pairs. For example, the
PCHL instruction exchanges the contents of the program counter with the contents
of the H and L registers.
Immediate Addressing:
Instructions that use immediate addressing have data assembled as a part of the
instruction itself. For example, the instruction CPI 'C' may be interpreted as
‘compare the contents of the accumulator with the letter C. When assembled, this
instruction has the hexadecimal value FE43. Hexadecimal 43 is the internal
representation for the letter C. When this instruction is executed, the processor
fetches the first instruction byte and determines that it must fetch one more byte.
The processor fetches the next byte into one of its internal registers and then
performs the compare operation.
ADDRESSING MODES
CONTD… Direct Addressing:
Jump instructions include a 16-bit address as part of the instruction. For example, the instruction JMP 1000H causes a jump to the hexadecimal address 1000 by replacing the current contents of the program counter with the new value 1000H.
Instructions that include a direct address require three bytes of storage: one for the instruction code, and two for the 16-bit address
Register Indirect Addressing:
Register indirect instructions reference memory via a register pair. Thus, the instruction MOV M,C moves the contents of the C register into the memory address stored in the H and L register pair. The instruction LDAX B loads the accumulator with the byte of data specified by the address in the B and C register pair.
UNIT- II
Intel 8086 microprocessor
Architecture
Signals
Instruction set
Addressing modes
Assembler directives
Assembly language programming
Procedures
Macros
Interrupts and interrupt service routines.
BIOS Function Calls
8086 ARCHITECTURE&PIN
DIAGRAM
8086 FEATURES
16-bit Arithmetic Logic Unit
16-bit data bus (8088 has 8-bit data bus)
20-bit address bus - 220 = 1,048,576 = 1 meg
The address refers to a byte in memory.
In the 8088, these bytes come in on the 8-bit data bus. In the 8086, bytes at
even addresses come in on the low half of the data bus (bits 0-7) and bytes at
odd addresses come in on the upper half of the data bus (bits 8-15).
The 8086 can read a 16-bit word at an even address in one operation and at an
odd address in two operations. The 8088 needs two operations in either case.
The least significant byte of a word on an 8086 family microprocessor is at the
lower address.
16-bit Registers
CS
SS
DS
ES
Segment
BP
Index
SP
SI
DI
AH
BH
CH
DH DL
CL
BL
AL
General Purpose
Status and Control
Flags
IP
AX
BX
CX
DX
8086 ARCHITECTURE
The 8086 has two parts,
the Bus Interface Unit (BIU) and
the Execution Unit (EU).
The BIU fetches instructions, reads and writes data, and computes the 20-bit address.
The EU decodes and executes the instructions using the 16-bit ALU.
The BIU contains the following registers:
IP - the Instruction Pointer
CS - the Code Segment Register
DS - the Data Segment Register
SS - the Stack Segment Register
ES - the Extra Segment Register
The BIU fetches instructions using the CS and IP, written CS:IP, to contract
the 20-bit address. Data is fetched using a segment register (usually the DS)
and an effective address (EA) computed by the EU depending on the
addressing mode.
INTERNAL BLOCK
PROGRAM MODEL
8086 Programmer’s Model
ES
CS
SS
DS
IP
AH
BH
CH
DH
AL
BL
CL
DL
SP
BP
SI
DI
FLAGS
AX
BX
CX
DX
Extra Segment
Code Segment
Stack Segment
Data Segment
Instruction Pointer
Accumulator
Base Register
Count Register
Data Register
Stack Pointer
Base Pointer
Source Index Register
Destination Index Register
BIU registers (20 bit adder)
EU registers
8086/88 internal registers 16 bits (2 bytes each)
AX, BX, CX and DX are two
bytes wide and each byte can
be accessed separately
These registers are used as
memory pointers.
Flags will be discussed later
Segment registers are used
as base address for a segment
in the 1 M byte of memory
The 8086/8088 Microprocessors: Registers
• Registers
– Registers are in the CPU and are referred to by specific names
– Data registers
• Hold data for an operation to be performed
• There are 4 data registers (AX, BX, CX, DX)
– Address registers
• Hold the address of an instruction or data element
• Segment registers (CS, DS, ES, SS)
• Pointer registers (SP, BP, IP)
• Index registers (SI, DI)
– Status register
• Keeps the current status of the processor
• On an IBM PC the status register is called the FLAGS register
– In total there are fourteen 16-bit registers in an 8086/8088
Data Registers: AX, BX, CX, DX
• Instructions execute faster if the data is in a register
• AX, BX, CX, DX are the data registers
• Low and High bytes of the data registers can be accessed
separately
– AH, BH, CH, DH are the high bytes
– AL, BL, CL, and DL are the low bytes
• Data Registers are general purpose registers but they also
perform special functions
• AX
– Accumulator Register
– Preferred register to use in arithmetic, logic and data transfer instructions
because it generates the shortest Machine Language Code
– Must be used in multiplication and division operations
– Must also be used in I/O operations
• BX
– Base Register
– Also serves as an address register
– Used in array operations
– Used in Table Lookup operations (XLAT)
• CX
– Count register
– Used as a loop counter
– Used in shift and rotate operations
• DX
– Data register
– Used in multiplication and division
– Also used in I/O operations
Pointer and Index Registers
• Contain the offset addresses of memory locations
• Can also be used in arithmetic and other operations
• SP: Stack pointer
– Used with SS to access the stack segment
• BP: Base Pointer
– Primarily used to access data on the stack
– Can be used to access data in other segments
• SI: Source Index register
– is required for some string operations
– When string operations are performed, the SI register points to
memory locations in the data segment which is addressed by the
DS register. Thus, SI is associated with the DS in string
operations.
• DI: Destination Index register – is also required for some string operations.
– When string operations are performed, the DI register points to
memory locations in the data segment which is addressed by the
ES register. Thus, DI is associated with the ES in string
operations.
• The SI and the DI registers may also be used to access data
stored in arrays
Segment Registers - CS, DS, SS and ES
• Are Address registers
• Store the memory addresses of instructions and data
• Memory Organization
– Each byte in memory has a 20 bit address starting with 0 to 220-1 or 1
meg of addressable memory
– Addresses are expressed as 5 hex digits from 00000 - FFFFF
– Problem: But 20 bit addresses are TOO BIG to fit in 16 bit registers!
– Solution: Memory Segment
• Block of 64K (65,536) consecutive memory bytes
• A segment number is a 16 bit number
• Segment numbers range from 0000 to FFFF
• Within a segment, a particular memory location is specified with an offset
• An offset also ranges from 0000 to FFFF
Segmented Memory
Segmented memory addressing: absolute (linear) address is a combination of a 16-bit segment value added to a 16-bit offset
00000
10000
20000
30000
40000
50000
60000
70000
80000
90000
A0000
B0000
C0000
D0000
E0000
F0000
8000:0000
8000:FFFF
seg ofs
8000:0250
0250
one segment
Memory Address Generation
• The BIU has a dedicated adder for
determining physical memory addresses
Intel
Physical Address (20 Bits)
Adder
Segment Register (16 bits) 0 0 0 0
Offset Value (16 bits)
Example Address Calculation
• If the data segment starts at location 1000h and a data reference contains the address 29h where is the actual data?
Intel
Offset: 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 1
2 9
0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Segment:
0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 1 Address:
SEGMENT:OFFSET ADDRESS
• Logical Address is specified as segment:offset
• Physical address is obtained by shifting the segment address 4
bits to the left and adding the offset address
• Thus the physical address of the logical address A4FB:4872 is
A4FB0
+ 4872
A9822
EXAMPLE
Segment Register Offset Physical or Absolute Address
CS:IP = 400:56 Logical Address
0H
0FFFFFH
Memory 0
+
CS:
IP
0400H
0056H
4000H
4056H
0400
0056
04056H
The offset is the distance in bytes from the start of the segment. The offset is given by the IP for the Code Segment. Instructions are always fetched with using the CS register.
The physical address is also called the absolute address.
THE CODE SEGMENT
THE DATA SEGMENT
Data is usually fetched with respect to the DS register. The effective address (EA) is the offset. The EA depends on the addressing mode.
Memory
Segment Register Offset Physical Address
+
DS:
EA
05C0
0050
05C00H
05C50H
05C0 0
0050
05C50H
DS:EA
0H
0FFFFFH
THE STACK SEGMENT
Segment Register Offset Physical Address
Memory
+
SS:
SP
0A00
0100
0A000H
0A100H
0A00 0
0100
0A100H
The stack is always referenced with respect to the stack segment register. The stack grows toward decreasing memory locations. The SP points to the last or top item on the stack. PUSH - pre-decrement the SP POP - post-increment the SP
The offset is given by the SP register.
SS:SP
0H
0FFFFFH
Carry flag
Parity flag
Auxiliary flag
Zero
Overflow
Direction
Interrupt enable
Trap
Sign 6 are status flags
3 are control flag
Flags
• CF (carry) Contains carry from leftmost bit following
arithmetic, also contains last bit from a shift or rotate
operation.
Flag Register
Flag O D I T S Z A P C
Bit no. 15 14 13 12 11 1
0 9 8 7 6 5 4 3 2 1 0
• Conditional flags:
– They are set according to some results of arithmetic operation. You do
not need to alter the value yourself.
• Control flags:
– Used to control some operations of the MPU. These flags are to be set
by you in order to achieve some specific purposes.
Flag Register
OF (overflow) Indicates overflow of the leftmost bit during arithmetic.
DF (direction) Indicates left or right for moving or comparing string data.
IF (interrupt) Indicates whether external interrupts are being processed or
ignored.
TF (trap) Permits operation of the processor in single step mode.
SF (sign) Contains the resulting sign of an arithmetic operation (1=negative)
ZF (zero) Indicates when the result of arithmetic or a comparison is zero.
(1=yes)
AF (auxiliary carry) Contains carry out of bit 3 into bit 4 for specialized
arithmetic.
PF (parity) Indicates the number of 1 bits that result from an operation.
Macros
avoid repetitious SAS code
create generalizable and flexible SAS code
pass information from one part of a SAS job to another
conditionally execute data steps and PROCs
dynamically create code at execution time
Example
Simple macro variable
%let dsn=LAB;
title "DATA SET &dsn";
proc contents data=&dsn;
run;
proc print data=&dsn(obs=10);
run;
Procedures
Initial call to run an external program
Run a LCA model to simulate data
Estimate a model of simulated data
Collect necessary output
Check if output read is indeed output wanted
Collect output in a single data matrix
Instruction Set
Mov destination, source
add, inc, dec and sub instructions
Input/Output
String Instructions
Machine Control
Flag Manipulation.
Addressing Modes
Immediate addressing.
Register addressing.
Direct addressing.
Indirect addressing
Implied addressing.
Indexed addressing
Relative addressing
Interrupts &Interrupt Service
Routine
An interrupt signals the processor to suspend its current activity
(i.e. running your program) and to pass control to an interrupt service program (i.e. part of the operating system).
A software interrupt is one generated by a program (as opposed to
one generated by hardware).
The 8086 int instruction generates a software interrupt.
It uses a single operand which is a number indicating which MSDOS
subprogram is to be invoked.
This subprogram handles a variety of I/O operations by calling
appropriate subprograms.
MAXIMUM MODE
Maximum mode
Maximum mode is designed to be used with a coprocessor exists in the system.
All the control signals (except RD) are not generated by the microprocessor.
But we still need those control signals.
Solution:
8288.
8086 maximum & minimum
modes
8086 maximum & minimum modes
The mode is controlled by MN/MX.
Maximum mode is obtained by connecting MN/MX to low and minimum mode is by connecting it to high.
Having two different modes (minimum and maximum) is used only 8088/8086.
Each mode enables a different control structure.
Minimum mode operation and control signals are very similar to those of 8085.
So 8085 8-bit peripherals can be used with 8086 without special considerations.
Easy and least expensive way to build single processor systems
S2 S1 S0 operation signal 0 0 0 Interrupt Acknowledge INTA
0 0 1 Read I/O port IORC
0 1 0 Write I/O port IOWC, AIOWC
0 1 1 Halt none
1 0 0 Instruction Fetch MRDC
1 0 1 Read Memory MRDC
1 1 0 Write Memory MWTC, AMWC
1 1 1 Passive none
UNIT III
Coprocessor Configuration
Closely Coupled Configuration
Loosely Coupled Configuration
8087 Numeric Data Processor-architecture
Data types
8089 I/O Processor-Architecture
Communication between CPU and IOP
PIN DIAGRAM OF 8087
UNIT V
Architecture of 8051
Signals
Operational features
Memory and I/O addressing
Interrupts
Instruction set
Applications.
RAM ROM
I/O
Port Timer
Serial
COM
Port Microcontroller
CPU
A smaller computer
On-chip RAM, ROM, I/O ports...
Example:Motorola’s 6811, Intel’s 8051, Zilog’s Z8 and PIC
16X
A single chip
Microcontroller :
Microprocessor
CPU is stand-alone, RAM,
ROM, I/O, timer are separate
designer can decide on the
amount of ROM, RAM and
I/O ports.
expansive
versatility
general-purpose
Microcontroller
• CPU, RAM, ROM, I/O and
timer are all on a single chip
• fix amount of on-chip ROM,
RAM, I/O ports
• for applications in which cost,
power and space are critical
• single-purpose
Microprocessor vs. Microcontroller
Block Diagram
CPU
On-chip
RAM
On-chip
ROM for
program
code
4 I/O Ports
Timer 0
Serial
Port OSC
Interrupt
Control
External interrupts
Timer 1
Timer/Counter
Bus
Control
TxD RxD P0 P1 P2 P3
Address/Data
Counter
Inputs
Pin Description of the 8051
1 2 3
4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
40 39 38
37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21
P1.0 P1.1 P1.2
P1.3 P1.4 P1.5 P1.6 P1.7 RST
(RXD)P3.0 (TXD)P3.1
(T0)P3.4 (T1)P3.5
XTAL2 XTAL1
GND
(INT0)P3.2
(INT1)P3.3
(RD)P3.7 (WR)P3.6
Vcc P0.0(AD0) P0.1(AD1)
P0.2(AD2) P0.3(AD3) P0.4(AD4) P0.5(AD5) P0.6(AD6) P0.7(AD7)
EA/VPP ALE/PROG
PSEN P2.7(A15) P2.6(A14) P2.5(A13) P2.4(A12) P2.3(A11) P2.2(A10) P2.1(A9) P2.0(A8)
8051
(8031)
Figure (b). Power-On RESET Circuit
30 pF
30 pF
8.2 K
10 uF
+
Vcc
11.0592 MHz
EA/VPP X1
X2
RST
31
19
18
9
Port 0 with Pull-Up Resistors
P0.0 P0.1 P0.2 P0.3 P0.4 P0.5 P0.6 P0.7
DS5000
8751
8951
Vcc 10 K
Po
rt
0
Registers
A
B
R0
R1
R3
R4
R2
R5
R7
R6
DPH DPL
PC
DPTR
PC
Some 8051 16-bit Register
Some 8-bitt Registers of
the 8051
Stack in the 8051
The register used to access the stack is called SP (stack pointer) register.
The stack pointer in the 8051 is only 8 bits wide, which means that it can take value 00 to FFH. When 8051 powered up, the SP register contains value 07.
7FH
30H
2FH
20H
1FH
17H
10H
0FH
07H
08H
18H
00H Register Bank 0
(Stack) Register Bank 1
Register Bank 2
Register Bank 3
Bit-Addressable RAM
Scratch pad RAM
Timer : : Timer:
Interrupt :
Numerical Bases Used in
Programming
Hexadecimal
Binary
BCD
Hexadecimal Basis
Hexadecimal Digits:
1 2 3 4 5 6 7 8 9 A B C D E F
A=10
B=11
C=12
D=13
E=14
F=15
Decimal, Binary, BCD, & Hexadecimal Numbers
(43)10=
(0100 0011)BCD=
( 0010 1011 )2 =
( 2 B )16
Register Addressing Mode
MOV Rn, A ;n=0,..,7
ADD A, Rn
MOV DPL, R6
MOV DPTR, A
MOV Rm, Rn
Direct Addressing Mode
Although the entire of 128 bytes of RAM can be accessed using direct addressing mode, it is most often used to access RAM loc. 30 – 7FH.
MOV R0, 40H
MOV 56H, A
MOV A, 4 ; ≡ MOV A, R4
MOV 6, 2 ; copy R2 to R6
; MOV R6,R2 is invalid !
Immediate Addressing Mode
MOV A,#65H
MOV R6,#65H
MOV DPTR,#2343H
MOV P1,#65H
SETB bit ; bit=1
CLR bit ; bit=0
SETB C ; CY=1
SETB P0.0 ;bit 0 from port 0 =1
SETB P3.7 ;bit 7 from port 3 =1
SETB ACC.2 ;bit 2 from ACCUMULATOR =1
SETB 05 ;set high D5 of RAM loc. 20h
Note:
CLR instruction is as same as SETB
i.e.:
CLR C ;CY=0
But following instruction is only for CLR:
CLR A ;A=0
DEC byte ;byte=byte-1
INC byte ;byte=byte+1
INC R7
DEC A
DEC 40H ; [40]=[40]-1
LOOP and JUMP Instructions
JZ Jump if A=0
JNZ Jump if A/=0
DJNZ Decrement and jump if A/=0
CJNE A,byte Jump if A/=byte
CJNE reg,#data Jump if byte/=#data
JC Jump if CY=1
JNC Jump if CY=0
JB Jump if bit=1
JNB Jump if bit=0
JBC Jump if bit=1 and clear bit
Conditional Jumps :
Call instruction
SETB P0.0
.
.
CALL UP
.
.
.
CLR P0.0
.
.
RET
UP:
UNIT IV
Memory Interfacing and I/O interfacing
Parallel communication interface
Serial communication interface
Timer
Keyboard /display controller
Interrupt controller
DMA controller
Programming and applications
Accessing I/O Devices
I/O address mapping
Memory-mapped I/O Reading and writing are similar to memory
read/write
Uses same memory read and write signals
Most processors use this I/O mapping
Isolated I/O Separate I/O address space
Separate I/O read and write signals are needed
Pentium supports isolated I/O 64 KB address space
Can be any combination of 8-, 16- and 32-bit I/O ports
Also supports memory-mapped I/O
Accessing I/O Devices
(cont’d)
Accessing I/O ports in Pentium
Register I/O instructions in accumulator, port8 ; direct format
Useful to access first 256 ports
in accumulator,DX ; indirect format
DX gives the port address
Block I/O instructions ins and outs
Both take no operands---as in string instructions
ins: port address in DX, memory address in ES:(E)DI
outs: port address in DX, memory address in ES:(E)SI
We can use rep prefix for block transfer of data
An Example I/O Device
Keyboard
Keyboard controller scans and reports
Key depressions and releases
Supplies key identity as a scan code
Scan code is like a sequence number of the key
Key’s scan code depends on its position on the
keyboard
No relation to the ASCII value of the key
Interfaced through an 8-bit parallel I/O port
Originally supported by 8255 programmable
peripheral interface chip (PPI)
An Example I/O Device
(cont’d)
8255 PPI has three 8-bit registers Port A (PA)
Port B (PB)
Port C (PC)
These ports are mapped as follows
8255 register Port address
PA (input port) 60H
PB (output port) 61H
PC (input port) 62H
Command register 63H
An Example I/O Device
(cont’d)
Mapping of 8255 I/O ports
An Example I/O Device
(cont’d)
Mapping I/O ports is similar to mapping memory
Partial mapping
Full mapping See our discussion in Chapter 16
Keyboard scan code and status can be read from port 60H
7-bit scan code is available from PA0 – PA6
Key status is available from PA7 PA7 = 0 – key depressed
PA0 = 1 – key released
I/O Data Transfer
Data transfer involves two phases
A data transfer phase It can be done either by
Programmed I/O
DMA
An end-notification phase Programmed I/O
Interrupt
Three basic techniques
Programmed I/O
DMA
Interrupt-driven I/O (discussed in Chapter 20)
I/O Data Transfer (cont’d)
Programmed I/O
Done by busy-waiting This process is called polling
Example
Reading a key from the keyboard involves Waiting for PA7 bit to go low
Indicates that a key is pressed
Reading the key scan code
Translating it to the ASCII value
Waiting until the key is released
Program 19.1 uses this process to read input from the keyboard
I/O Data Transfer (cont’d)
Direct memory access (DMA)
Problems with programmed I/O
Processor wastes time polling
In our example
Waiting for a key to be pressed,
Waiting for it to be released
May not satisfy timing constraints associated with
some devices
Disk read or write
DMA
Frees the processor of the data transfer
responsibility
I/O Data Transfer (cont’d)
I/O Data Transfer (cont’d)
DMA is implemented using a DMA
controller
DMA controller
Acts as slave to processor
Receives instructions from processor
Example: Reading from an I/O device
Processor gives details to the DMA controller
I/O device number
Main memory buffer address
Number of bytes to transfer
Direction of transfer (memory I/O device, or vice
versa)
I/O Data Transfer (cont’d)
Steps in a DMA operation Processor initiates the DMA controller Gives device number, memory buffer pointer, …
Called channel initialization
Once initialized, it is ready for data transfer
When ready, I/O device informs the DMA controller DMA controller starts the data transfer process
Obtains bus by going through bus arbitration
Places memory address and appropriate control signals
Completes transfer and releases the bus
Updates memory address and count value
If more to read, loops back to repeat the process
Notify the processor when done Typically uses an interrupt
I/O Data Transfer (cont’d)
DMA controller details
I/O Data Transfer (cont’d)
DMA transfer timing
I/O Data Transfer (cont’d)
8237 DMA controller
I/O Data Transfer (cont’d)
8237 supports four DMA channels
It has the following internal registers
Current address register
One 16-bit register for each channel
Holds address for the current DMA transfer
Current word register
Keeps the byte count
Generates terminal count (TC) signal when the count goes from
zero to FFFFH
Command register
Used to program 8257 (type of priority, …)
I/O Data Transfer (cont’d)
Mode register Each channel can be programmed to
Read or write
Autoincrement or autodecrement the address
Autoinitialize the channel
Request register For software-initiated DMA
Mask register Used to disable a specific channel
Status register
Temporary register Used for memory-to-memory transfers
What is a Timer?
A device that uses highspeed clock input
to provide a series of time or count-related
events
÷ 000000
0x1206
I/O Control
Clock Divider
Counter Register
Reload
on Zero
Countdown Register
Interrupt to
Processor
System Clock
Inside the Timer
High Byte Low Byte Counter Register at offsets 0x04, 0x00 (write only)
Current Counter (not directly readable by software)
GO Register offset 0x08, immediately moves
Counter Reg value into Current Counter
Latch Register offset 0x0C, write a ``1'' to immediately write
Current Counter value to readable Latch Reg
Latched Counter
at offsets 0x04, 0x00 (read only)
Setting the Timer's
Counter Registers
Counter is usually programmed to reach
zero X times per second
To program the timer to reach zero 100 times
per second
Example: For a 2 MHz-based timer, 2MHz /
100 = 20,000
#define TIMER1 0x10200050
int time;
time = 2000000 / 100;
timer = (timer_p) TIMER1;
timer>countLow = (unsigned char) (time &
0xff);
timer>countHigh = (unsigned char) ((time
> 8) & 0xff);
timer>go = (unsigned char) 0x1;
Interrupt vs. Polled I/O
Polled I/O requires the CPU to ask a device (e.g. toggle switches) if the device requires
servicing
For example, if the toggle switches have changed position
Software plans for polling the devices and is written to know when a device will be
serviced
Interrupt I/O allows the device to interrupt the processor, announcing that the device
requires attention
This allows the CPU to ignore devices unless they request servicing (via interrupts)
Software cannot plan for an interrupt because interrupts can happen at any time
therefore, software has no idea when an interrupt will occur
This makes it more difficult to write code
Processors can be programmed to ignore interrupts
We call this masking of interrupts
Different types of interrupts can be masked (IRQ vs. FIQ)
IRQ and FIQ
Program Status Register
To disable interrupts, set the corresponding “F” or “I” bit to 1
On interrupt, processor switches to FIQ32_mode registers or IRQ32_mode
registers
On any interrupt (or) Switch register banks
Copy PC and CPSR to R14 and SPSR
Change new CPSR mode bits
SWI Trap
N
31 30 29 28 27 … 8 7 6 5 4 3 2 1 0
Z C V I F M4 M3 M2 M1 M0
INTERFACING
Static RAM interfacing.
Procedure
Configuration.
Dynamic RAM interfacing.
I/O Port Interfacing
Steps in Interfacing
Methods of interfacing
a) I/O Mapped
b) Memory Mapped.
PIO 8255
Programmable input output Port.
Architecture
Signals
Modes Of Operation
a) BSR Mode
b) I/O Modes
i) Mode 0(Basic I/O Mode)
ii) Mode 1 (Strobed I/O Mode)
iii) Mode 2 (Strobed Bidirectional Mode)
Controller 8259
Programmable Interrupt Controller.
Architecture and Signal Descriptions
Interrupt Sequence .
Command word
a) Initialization Command word (ICWs).
b) Operation Command words.
Modes of operation:
1.Nested mode.
2.Fully Nested Mode.
3.Poll mode
Automatic EOI Mode.
Display Controller 8279
Output Mode
1)Display Scan
2) Display Entry
Command words.
8251 USART
Methods of Data communication
a) Simplex
b) Duplex
c) Half Duplex
Architecture
Control Word
a) Mode Instruction control word
b) Command instruction control word