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2 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.

3 OBJECTIVE  To study the architecture and Instruction set of 8085 and 8086  To develop assembly language programs in 8085 and  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.

4 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

5 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.

6 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).


8 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


10 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

11 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)

12 8085 Instruction Types




16 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.

17 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.

18 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


20 8086 FEATURES  16-bit Arithmetic Logic Unit  16-bit data bus (8088 has 8-bit data bus)  20-bit address bus = 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.

21 16-bit Registers

22 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.


24 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

25 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. 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

26 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

27 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

28 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

29 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.

30 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

31 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 or 1 meg of addressable memory –Addresses are expressed as 5 hex digits from 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


33 Segmented Memory Segmented memory addressing: absolute (linear) address is a combination of a 16-bit segment value added to a 16-bit offset linear addresses one segment

34 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 Offset Value (16 bits)

35 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: Segment: Address:

36 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 A4FB A9822


38 Segment Register Offset Physical or Absolute Address CS:IP = 400:56 Logical Address 0H 0FFFFFH Memory 0 + CS: IP 0400H 0056H 4000H 4056H H 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

39 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 05C C00H 05C50H 05C C50H DS:EA 0H 0FFFFFH

40 THE STACK SEGMENT Segment Register Offset Physical Address Memory + SS: SP 0A A000H 0A100H 0A A100H 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

41 Carry flag Parity flag Auxiliary flag Zero Overflow Direction Interrupt enable Trap Sign 6 are status flags 3 are control flag Flags

42 CF (carry) Contains carry from leftmost bit following arithmetic, also contains last bit from a shift or rotate operation. Flag Register FlagODITSZAPC Bit no 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.

43 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.

44  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.

45 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

46 Example Simple macro variable %let dsn=LAB; title "DATA SET &dsn"; proc contents data=&dsn; run; proc print data=&dsn(obs=10); run;

47 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

48 Instruction Set  Mov destination, source  add, inc, dec and sub instructions  Input/Output  String Instructions  Machine Control  Flag Manipulation.

49 Addressing Modes  Immediate addressing.  Register addressing.  Direct addressing.  Indirect addressing  Implied addressing.  Indexed addressing  Relative addressing

50 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.

51 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.

52 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  So bit peripherals can be used with 8086 without special considerations.  Easy and least expensive way to build single processor systems


54 S2 S1 S0 operationsignal Interrupt AcknowledgeINTA Read I/O portIORC Write I/O portIOWC, AIOWC Haltnone Instruction FetchMRDC Read MemoryMRDC Write MemoryMWTC, AMWC Passivenone


56 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


58 Architecture of 8087  Two Units  Control Unit  Execution Unit


60 Control Unit  Control unit: To synchronize the operation of the coprocessor and the processor.  This unit has a Control word and Status word and Data Buffer  If instruction is an ESCape (coprocessor) instruction, the coprocessor executes it, if not  the microprocessor executes.  Status register reflects the over all operation of the coprocessor. Status Register

61  C3-C0 Condition code bits  TOP Top-of-stack (ST)  ES Error summary  PE Precision error  UE Under flow error  OE Overflow error  ZE Zero error  DE Denormalized error  IE Invalid error  B Busy bit B-Busy bit indicates that coprocessor is busy executing a task. Busy can be tested by examining the status or by using the FWAIT instruction. C3-C0 Condition code bits indicates conditions about the coprocessor. TOP- Top of the stack (ST) bit indicates the current register address as the top of the stack. ES-Error summary bit is set if any unmasked error bit (PE, UE, OE, ZE, DE, or IE) is set. In the 8087 the error summary is also caused a coprocessor interrupt. PE- Precision error indicates that the result or operand executes selected precision. UE-Under flow error indicates the result is too large to be represent with the current precision selected by the control word. OE-Over flow error indicates a result that is too large to be represented. If this error is masked, the coprocessor generates infinity for an overflow error. ZE-A Zero error indicates the divisor was zero while the dividend is a non-infinity or non-zero number. DE-Denormalized error indicates at least one of the operand is denormalized. IE-Invalid error indicates a stack overflow or underflow, indeterminate from (0/0,0,-0, etc) or the use of a NAN as an operand. This flag indicates error such as those produced by taking the square root of a negative number.

62 CONTROL REGISTER  Control register selects precision, rounding control, infinity control.  It also masks an unmasks the exception bits that correspond to the rightmost Six bits of status register.  Instruction FLDCW is used to load the value into the control register.  IC Infinity control  RC Rounding control  PC Precision control  PM Precision control  UM Underflow mask  OM Overflow mask  ZM Division by zero mask  DM Denormalized operand mask  IM Invalid operand mask

63  IC –Infinity control selects either affine or projective infinity. Affine allows positive and negative infinity, while projective assumes infinity is unsigned.  INFINITY CONTROL 0 = Projective 1 = Affine  RC –Rounding control determines the type of rounding.  ROUNDING CONTROL 00=Round to nearest or even 01=Round down towards minus infinity 10=Round up towards plus infinity 11=Chop or truncate towards zero  PC- Precision control sets the precision of he result as define in table  PRECISION CONTROL 00=Single precision (short) 01=Reserved 10=Double precision (long) 11=Extended precision (temporary)  Exception Masks – It Determines whether the error indicated by the exception affects the error bit in the status register. If a logic1 is placed in one of the exception control bits, corresponding status register bit is masked off.

64 Numeric Execution Unit  This performs all operations that access and manipulate the numeric data in the coprocessor’s registers.  Numeric registers in NUE are 80 bits wide.  NUE is able to perform arithmetic, logical and transcendental operations as well as supply a small number of mathematical constants from its on-chip ROM.  Numeric data is routed into two parts ways a 64 bit mantissa bus and a 16 bit sign/exponent bus.

65 Data Types  Internally, all data operands are converted to the 80-bit temporary real format. We have 3 types.  Integer data type  Packed BCD data type  Real data type Example Converting a decimal number into a Floating-point number. 1) Converting the decimal number into binary form. 2) Normalize the binary number 3) Calculate the biased exponent. 4) Store the number in the floating-point format. Example  Step Result 1) ) = * 26 3) = ) Sign = 0  Exponent =  Significand =  In step 3 the biased exponent is the exponent a 26 or 110,plus a bias of (7FH) single precision no use 7F and double precision no use 3FFFH.  IN step 4 the information found in prior step is combined to form the floating point no.

66 UNIT V  Architecture of 8051  Signals  Operational features  Memory and I/O addressing  Interrupts  Instruction set  Applications.

67 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 :

68 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

69 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

70 Pin Description of the 8051 

71 Figure (b). Power-On RESET Circuit 30 pF 8.2 K 10 uF + Vcc MHz EA/VPP X1 X2 RST 

72 Port 0 with Pull-Up Resistors

73 Registers A B R0 R1 R3 R4 R2 R5 R7 R6 DPHDPL PC DPTR PC Some bit Register Some 8-bitt Registers of the 8051

74 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

75 Timer : :

76 Interrupt :

77 Numerical Bases Used in Programming  Hexadecimal  Binary  BCD

78 Hexadecimal Basis  Hexadecimal Digits: A B C D E F A=10 B=11 C=12 D=13 E=14 F=15

79 Decimal, Binary, BCD, & Hexadecimal Numbers (43) 10 = ( ) BCD = ( ) 2 = ( 2 B ) 16

80 Register Addressing Mode MOVRn, A;n=0,..,7 ADDA, Rn MOVDPL, R6 MOVDPTR, A MOVRm, Rn

81 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. MOVR0, 40H MOV56H, A MOVA, 4; ≡ MOV A, R4 MOV6, 2; copy R2 to R6 ; MOV R6,R2 is invalid !

82 Immediate Addressing Mode MOVA,#65H MOVR6,#65H MOVDPTR,#2343H MOVP1,#65H

83 SETBbit; bit=1 CLRbit; bit=0 SETBC; CY=1 SETBP0.0;bit 0 from port 0 =1 SETBP3.7;bit 7 from port 3 =1 SETBACC.2;bit 2 from ACCUMULATOR =1 SETB05;set high D5 of RAM loc. 20h Note: CLR instruction is as same as SETB i.e.: CLRC;CY=0 But following instruction is only for CLR: CLRA;A=0

84 DECbyte;byte=byte-1 INCbyte;byte=byte+1 INCR7 DECA DEC40H; [40]=[40]-1

85 LOOP and JUMP Instructions JZJump if A=0 JNZJump if A/=0 DJNZDecrement and jump if A/=0 CJNE A,byteJump if A/=byte CJNE reg,#dataJump if byte/=#data JCJump if CY=1 JNCJump if CY=0 JBJump if bit=1 JNBJump if bit=0 JBCJump if bit=1 and clear bit Conditional Jumps :

86 Call instruction SETB P0.0. CALL UP. CLR P0.0. RET UP:

87 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

88 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

89 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

90 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)

91 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 register63H

92 An Example I/O Device (cont’d) Mapping of 8255 I/O ports

93 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

94 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)

95 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

96 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

97 I/O Data Transfer (cont’d)

98  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)

99 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

100 I/O Data Transfer (cont’d) DMA controller details

101 I/O Data Transfer (cont’d) DMA transfer timing

102 I/O Data Transfer (cont’d) 8237 DMA controller

103 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, …)

104 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

105 What is a Timer?  A device that uses high ­ speed clock input to provide a series of time or count-related events ÷ x1206 I/O Control Clock Divider Counter Register Reload on Zero Countdown Register Interrupt to Processor System Clock

106 Inside the Timer High ByteLow 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)

107 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 0x int time; time = / 100; timer = (timer_p) TIMER1; timer­>countLow = (unsigned char) (time & 0xff); timer­>countHigh = (unsigned char) ((time > 8) & 0xff); timer­>go = (unsigned char) 0x1;

108 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)

109 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 … ZCVIFM4M3M2M1M0

110 INTERFACING  Static RAM interfacing.  Procedure  Configuration.  Dynamic RAM interfacing.

111 I/O Port Interfacing  Steps in Interfacing  Methods of interfacing a) I/O Mapped b) Memory Mapped.

112 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)

113 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.

114 Display Controller 8279  Output Mode 1)Display Scan 2) Display Entry  Command words.

115 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

116 TEXT BOOKS  Ramesh S.Gaonkar, “Microprocessor - Architecture, Programming and Applications with the 8085”, Penram International publishing private limited, fifth edition.  (UNIT-1: – Chapters 3,5,6 and programming examples from chapters 7-10)  A.K. Ray & K.M.Bhurchandi, “Advanced Microprocessors and peripherals- Architectures, Programming and Interfacing”, TMH, 2002 reprint. (UNITS 2 to 5: – Chapters 1-6, , 8, 16)

117 REFERENCES  Douglas V.Hall, “Microprocessors and Interfacing: Programming and Hardware”, TMH, Third edition  Yu-cheng Liu, Glenn A.Gibson, “Microcomputer systems: The 8086 / 8088 Family architecture, Programming and Design”, PHI 2003  Mohamed Ali Mazidi, Janice Gillispie Mazidi, “The 8051 microcontroller and embedded systems”, Pearson education, 2004.


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