1. Lecture # 11

2. Programmable Peripheral Interface (PPI)

3. Programmable Peripheral Interface (PPI)
Device Used as Parallel port Interface (I/O controller) is PPI

4. Programmable Peripheral Interface (PPI)
CPU
Parallel
I/O Device Printer
PPI

5. Accessing the Parallel Port Through BIOS Functions

6. Accessing the Parallel Port Through BIOS Functions
INT 17H
Services 00
Display Characters 01
Initialize Printer 02
Request Printer
DX register
Port Interface Number
0=LPT1,1=LPT2,2=LPT3

7. Accessing the Parallel Port Through BIOS Functions
All the function Return in AH the Current Printer Status 7 6 5 4 3 2 1
Time out
Printer Busy
Receive Mode Selected
Out of Paper
Transfer Error
Printer OffLine

8. Accessing the Parallel Port Through BIOS Functions
Time Out Byte
0040:0078
LPT1
0040:0079
LPT2
0040:007A
LPT3

9. Accessing the Parallel Port Through BIOS Functions
Specify the number of Attempts BIOS perform before giving a time out Error
This byte Varies Depending upon the speed of the PC
Busy =0 Printer is Busy
Busy =1 Printer is not Busy

10. Importance of the Status Byte

11. Importance of the Status Byte
If((pstate&0x29)!=0)or ((pstate&0x80)==0) or
((pstate&0x10)==0)
{printerok=FALSE;}
else
{printerok=TRUE;}

12. Importance of the Status Byte
17H/00H Write
a character on entry
AH=00
AL=ASCII code
DX=Interface#
On exit
AH=Status Byte
17H/01H Initialize Printer
on entry
AH=01
DX=Interface#
On exit
AH=Status Byte
17H/02H Get Printer Status
on entry
AH=02, DX=Interface# On exit AH=Status Byte

13. Printing Program

14. Printing Program REGS regs; FILE *fptr; void main(void) {
fptr=fopen(“c:\\temp\\abc.text”,”rb”);
regs.h.ah=1;
regs.x.dx=0;
int86(0x17,&regs,&regs);
while(!feof(fptr))
{regs.h.ah=2;
if ((regs.h.ah & 0x80)==0x80)
{ regs.h.ah=0;
regs.h.al=getc(fptr);
}}}

15. Printing Program 1 #include <dos.h> void interrupt (*old)( );
void interrupt newint ( );
main( ) {
old = getvect(0x17);
setvect(0x17,newint);
keep(0,1000); }
void interrupt new ()
{ if (_AH==0)
if ((_AL>='A')&&(_AL<='Z'))
return;
(*old)();

16. Printing Program 2 #include <dos.h> void interrupt (*old)( );
void interrupt newfunc ( );
main( ) {
old=getvect(0x17);
setvect(0x17,newfunc);
keep(0,1000); }
void interrupt newfunc( )
if (_AH==0)
if ( _AL != ‘ ‘ )
(*old)();

17. Printing Program 3 void interrupt (*old)( );
void interrupt newfunc ( );
main()
{ old=getvect(0x17);
setvect(0x17,newfunc);
keep(0,1000); }
void interrupt newfunc ( )
{ if ( _AH == 0 ) {
(*old)();
_AH=0;
else
Printing Program 3

18. Direct Parallel Port Programming

19. Direct Parallel Port Programming
BIOS support up to three parallel ports
Address of these LPT ports is Stored in BIOS Data Area
40:08
word
LPT1
40:0A
LPT2
40:0C
LPT3
40:0E
LPT4

20. Direct Parallel Port Programming Dump File Text

21. Direct Parallel Port Programming
unsigned int far * lpt =
(unsigned int far *) 0x ;
unsigned int temp;
temp=*(lpt);
*lpt=*(lpt + 1);
*(lpt + 1)=temp;

22. Direct Parallel Port Programming Port Registers
40:08 store the base address for lpt1
The parallel port interface has 3 ports internally
If the Base address is 0X378 then the three Ports will be 0x378,0x379 0x37A

23. Printer Data Port
Base +0 = Data Port 7 6 5 4 3 2 1

24. Printer Status Register
Base + 1 = Printer Status
Busy=0
ACK=0
PE=1
SL=1
ERR=0
Out of Paper
Printer Online
Printer is ready for Next Character
Printer is Busy

25. Printer Control Register
Printer Control Register = Base + 2 7 6 5 4 3 2 1
IRQ SI IN
ALF ST
IRQ ENABLE
initialize
Auto
Line
Field
Execute Interrupt
When ACK=0;
STROB
SELECT InLine
Turn Computer on line

26. Direct Parallel Port Programming
file *fptr;
unsigned far *base=(unsigned int far *)0x
void main ( ) {
fptr=fopen(“c:\\abc.txt”,”rb”);
while( ! feof (fptr) )
{ if(( inport (*base + 1 ) & 0x80) == 0x80)
outport(*base, getc(fptr));
outport((*base)+2, inport((*base+2) & 0xFE);
outport((*base)+2, inport((*base+2) | 0x01); } }}