1. mPMCI Introduction Basic block diagram of computer
What is a microprocessor?
Existing microprocessors
Basic concepts-
Address bus
Data bus
Control bus
Use of ALE
Memory segmentation etc.

2. Block Diagram of Computer

3. Unit - I
MSDOS FAT
Device Drivers
8255 – PPI

4. Ms-dos file system C:\>dir Volume in drive C has no label.
Volume Serial Number is 54CA-076A
Directory of C:\
08/01/ :16 AM AUTOEXEC.BAT
04/18/ :16 PM <DIR> CompleteChatApplication
03/11/ :41 PM CONFIG.SYS
03/11/ :45 PM <DIR> Documents and Settings
04/04/ :08 PM <DIR> MATLAB7
03/11/ :22 PM nvscnrpt.log
03/11/ :12 PM <DIR> Old Ibm Driver
04/09/ :20 PM <DIR> Program Files
04/09/ :58 AM qhdebug.log
03/11/ :19 PM <DIR> temp
04/19/ :28 PM <DIR> WINDOWS
4 File(s) bytes
7 Dir(s) 3,813,830,656 bytes free
C:\>

5. Fig.1 An MS-DOS File System Structure
Drive Identifier
Root Directory (‘ \ ’)
File A
Directory X
File B
Directory Y
File C
File D
Directory Z
File E
Fig.1 An MS-DOS File System Structure

6. D : \ VMP \ fasm \ EXAMPLES>
Root Directory
Sub-Directory
Current Drive Identifier Current Directory
This is called as “Path.”
A complete path from root directory, prefixed by a logical drive code and followed by a filename & extension is called as “Fully Qualified Filename”.

7. FAT(File Allocation Table)
The File Allocation Table itself is the area on the hard drive that stores information concerning every cluster on the drive. By storing this information in a single area, the operating system can find the nearest free sections of memory without searching the entire drive. This helps to avoid major wear and tear on the memory device.
The File Allocation Table system ensures that files can be found and accessed anywhere on a drive with minimal time spent seeking. This not only helps to minimize the wear on the physical components of the drive, it also ensures that files can be accessed quickly. This leads to increased performance and efficiency. The simplicity and availability of the FAT system make it ideal for use on memory devices that are accessed by many different operating systems.

8. FAT(File Allocation Table)
A File Allocation Table (FAT) is a system used by computers in order to store file information.
MS-DOS assigns, for each newly created file, groups of sectors from files area in powers of 2. These are called as “Allocation units” or “clusters”.
The no. of sectors/cluster is defined in BPB.
The FAT system stores information in a series of clusters.
Disk Type
Power of 2
Sectors/cluster
5.25” 180kb FD 1
5.25” 360kb FD 2
PC/AT fixed Disk 4
PC/XT fixed disk 3 8

9. FAT(File Allocation Table)contd…
FAT gives information about how he disk space in files area is used:
Space used for files
Space that is not in use
Space that can not be used due to defects
DOS maintains two or more identical copies of FAT.
FAT has a 32-bit entry for every cluster in the files area.
First two entries contain media descriptor value
Special code used in FAT:
‘EOF’
‘0’(i.e. Zero)
‘BAD’
Descriptor
Medium
0F0H
3.5” Floppy Disk, 2 sided, 18 sector
0F8H
Fixed Disk
0FCH
5.25” floppy disk,1 sided, 9 sector

10. Ms-dos boot record
A boot sector is the portion of a hard disk or floppy disk that has the code stored on it to boot special programs, and to reference other key features to keep the disk working. There are many types of boot sectors, but there are two main ones: the master boot record and the volume boot record. A master boot sector exists on a drive that has been partitioned, and it usually finds the active partition and run its own volume boot record. The volume boot record, in turn, often contains code to run the operating system on the computer.

11. E9XXXX OR EB XX 90
00H
OEM NAME & VERSION ( 8 BYTES)
03H
MSDOS VERSION 2.0
BYTES / SECTOR (2 BYTES)
0BH
SECTORS / ALLOCATION UNIT (1 BYTE)
0DH
RESERVED SECTORS, STARTING AT 0 (2 BYTES)
10H
NUMBER OF FATS ( 1 BYTE)
11H
NUMBER OF ROOT DIRECTORY ENTRIES(2 BYTES)
13H
TOTAL SECTORS IN LOGICAL VOLUME(2 BYTES)
15H
MEDIA DESCRIPTOR BYTE
16H
NUMBER OF SECTORS / FAT (2 BYTES)
18H
MSDOS VERSION 3.0
SECTORS / TRACK (2 BYTES)
1AH
NUMBER OF HEADS(2 BYTES)
1CH
NUMBER OF HIDDEN SECTORS(4 BYTES)
20H
MSDOS VERSION 4.0
TOTAL SECTORS IN LOGICAL VOLUME
(MSDOS 4.0 & VOLUME SIZE > 32MB)
24H
PHYSICAL DRIVE NUMBER
25H
ADDITIONAL MSDOS VERSION 4.0
INFORMATION
RESERVED
26H
EXTENDED BOOT SIGNATURE RECORD
27H
32 BIT BINARY VOLUME ID
2BH
VOLUME LABEL( 11 BYTES)
36H
RESERVED( 8 BYTES)
3EH
BOOT STRAP
BPB

12. Byte Capacity Media Size and Type
Media Descriptor: This byte provides information about the media being used. The following table lists some of the recognized media descriptor values and their associated media. Note that the media descriptor byte may be associated with more than one disk capacity.
Byte Capacity Media Size and Type
F MB 3.5-inch, 2-sided, 36-sector
F MB 3.5-inch, 2-sided, 18-sector
F9 720 KB 3.5-inch, 2-sided, 9-sector
F9 1.2 MB 5.25-inch, 2-sided, 15-sector
FD 360 KB 5.25-inch, 2-sided, 9-sector
FF 320 KB 5.25-inch, 2-sided, 8-sector
FC 180 KB 5.25-inch, 1-sided, 9-sector
FE 160 KB 5.25-inch, 1-sided, 8-sector
F Fixed disk

13. Interaction between user & hardware
User level
User applications
Various OS components
Device drivers
Device controllers
I/O devices
OS level
Hardware level

14. Device drivers
A device driver is a program that a computer's operating system uses to control a particular hardware device that is attached to a computer.
There are device drivers for printers, displays, CD-ROM readers, diskette drives, and so on.
In Windows operating systems, a device driver file usually has a file name suffix of DLL or EXE. A virtual device driver usually has the suffix of VXD.
There are 2 types:
Resident device drivers
Installable device drivers

15. Device drivers contd… DEVICE TYPES Block-oriented
information is stored in fixed sized blocks
transfers are made a block at a time
used for disks and tapes
Stream-oriented/character devices
transfer information as a stream of bytes
used for terminals, printers, communication ports, mouse, and most other devices that are not secondary storage

16. Device drivers contd… Accordingly, there are two types of
installable device drivers:
Block device drivers
Character device drivers
There are two modes of operation:
ASCII mode – waits for some special character such as CTRL+C,CTRL+Z etc.
Binary mode – reads/writes exact no. of requested bytes.

17. Structure of device driver
Device Driver Header
Strategy Routine(strat)
Interrupt Routine(intr)

18. Fig. General Structure Of MSDOS Installable Device Driver
INTERRUPT ROUTINE
INITIALIZATION
MEDIA CHECK
BUILD BPB
IOCTL READ & WRITE
STATUS
READ
WRITE, WRITE/VERIFY
OUTPUT UNTIL BUSY
FLUSH BUFFERS
DEVICE OPEN
DEVICE CLOSE
CHECK WHETHER REMOVABLE
GENERIC IOCTL
GET/SET LOGICAL DEVICE
STRATEGY ROUTINE
DEVICE DRIVER HEADER
Fig. General Structure Of MSDOS Installable Device Driver

19. FIG. DEVICE DRIVER HEADER
LINK TO NEXT DRIVER, OFFSET
02H
LINK TO NEXT DRIVER, SEGMENT
04H
DEVICE ATTRIBUTE WORD
06H
STRATEGY ENTRY POINT, OFFSET
08H
INTERRUPT ENTRY POINT, OFFSET
0AH
LOGICAL NAME(8-BYTES) IF CHARACTER DEVICE OR
NO. OF UNITS(1-BYTE) IF BLOCK DEVICE FOLLOWED BY RESERVED SPACE(7 BYTES)
FIG. DEVICE DRIVER HEADER

20. FIG. FORMAT OF REQUEST HEADER
Request Struc
Rlength db ?
Unit db ?
Command db ?
Status dw ?
Reserve db 8 Dup(?)
Media db ?
Address dd ?
Count dw ?
Sector dw ?
Request Ends
;request header template structure
;0 – length of Request header
;1 – unit no. For this request
;2 – request header’s command code
;3 – driver’s return status word
;5 – reserved area
;13 – Media descriptor byte
;14 – Memory address for transfer
;18 – byte/sector count value
;20 – starting sector value
;request header template ends
FIG. FORMAT OF REQUEST HEADER

21. Interrupt routine
A collection of subroutines to implement the various function types called command codes.
A centralized entry point – that saves all the affected registers, extracts the desired function code from the request header & branches to appropriate command code routine.
A centralized exit point – that stores status & error codes into the request header & restores the previous contents of the affected registers.

22. .com files
a COM file is a type of executable file; the name is derived from the file name extension .COM. Originally, the term stood for "Command file", a text file containing commands to be issued to the operating system.
The COM format is the original binary executable format used in CP/M and MS-DOS. It is very simple; it has no header, and contains no metadata, only code and data i.e.it resides on disk as absolute image.
Since it lacks relocation information, it is loaded by the operating system at a pre-set address, at offset 0x0100, where it is executed

23. .exe file No limit on size.
.exe program can be fit in the small,medium or large module in which segment register contain different value i.e. Code, data & stack will reside in different segments.
.EXE program may have multiple code & data segments.
A .EXE program resides in a special file with extension .EXE.
It also contains a unique header, checksum & relocation map etc.

24. .COM FILE
.EXE FILE
1. Max. Size of these programs is 64KB
1. They can be as large as available memory space.
2.In Intel 8086, .COM file is fixed in tiny module in which all segment register contain same value i.e. Code & data are mixed together.
2. .EXE program fit into small, medium or large module in which segment register contain different value
3. It reside on disk as absolute memory image in file.
3. It also contains a unique header, checksum & relocation map etc.

25. I/o port address decoder
Two methods are available:
1. I/O mapped I/O (isolated I/O)
• I/O Ports are isolated from memory in a separate I/O address
space.
• Memory can be expanded to full size
• Data transfer from/to I/O is restricted to IN and OUT
instructions.
Two forms:
1.Fixed Port
e.g. IN AL, 38h
IN AL, C000H
2.Variable Port
e.g. MOV DX,FFF8H
IN AL,DX
• Separate control signals using M/IO, WR, RD enable I/O ports.
• Intel-based PC’s use isolated I/O

26. I/o port address decoder contd…
2. Memory Mapped I/O
• I/O device is treated as a memory location.
• Any memory transfer instruction can used to access the device.
e.g.ADD AL,DS:BYTE PTR[0C000H]
• Reduces amount of system memory available to applications.
• Reserves fixed portion(s) of the memory map for I/O.
• 6800, uses memory-mapped I/O.

27. I/o port address decoderY0 Y1 Y2 Y3 Y4 Y5 Y6 Y7 A
A14
A15 G1
G2#
G3# C B A3

28. TRUTH TABLE FOR GIVEN ADDRESS DECODER- A6 A5 A4 A3 A2 A1 A0
PORT ADDRESS 1 X
C000
C008
C010
C018
C020
C028
C030
C038

29. Direct I/O v.s. Memory-Mapped I/O
FFFFF
FFFFF
Memory
addressing
space
I/O
FFFF
I/O
addressing
space
Memory addressing
space
00000
00000
0000
Memory-mapped I/O
Direct I/O
Direct I/O: I/O addresses are separated from memory address
Advantage: Do not take memory addressing space
Disadvantage: Use only AL or AX transferring data
Memory-mapped I/O: I/O ports are treated as memory locations
Advantage: Accessing I/O ports is like accessing memory locations Can use other instructions to access I/O ports
Disadvantage: Take memory addressing space

30. Methods of parallel data transfer
Simple I/O
Strobed I/O
SENDER
RECEIVER
DATA LINES
SENDER
RECEIVER
DATA LINES
STB

31. Pinout of 8255

32. 8255 ppi

33. Mode select control word

34. BSR control word

35. 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. The ports of the 8255 can be programmed in any of the following modes
It has three modes of operation

36. Mode 0(Basic Input/Output)
Simple I/O mode
Any of the ports A, B, CL, and CU can be
programmed as input or output
All bits are out or all are in
There is no control of individual bits

37. Mode 1(Strobed Input/Output)
Simple I/O with handshaking capabilities
Ports A and B can be used as input or
output ports with handshaking capabilities
Handshaking signals are provided by the
bits of port C
The device provides the handshaking signals
PA[7:0]
STBA
IBFA
INTRA
PC3
PC5
PC4
PB[7:0]
STBB
IBFB
INTRB
PC0
PC1
PC2
PC6, 7
8255
OBFA
ACKA
PC6
PC7
OBFB
ACKB
PC4, 5

38. Mode 2(Bi-Directional Bus)
Bidirectional port A with handshaking
capabilities
Port A can be used as a bidirectional I/O port with handshaking capabilities whose signals are provided by port C.
The device provides the handshaking signals
PA[7:0]
OBFA
ACKA
INTRA
PC4
PC6
PC7
STBA
IBFA
PC0
PC3
PC5
8255
PB[7:0]
In Out
Mode 0
STBB OBFB
IBFB ACKB
INTRB INTRB
Mode 1

39. Summary of modes