Lecture # 11
Programmable Peripheral Interface (PPI)
• Device Used as Parallel port Interface (I/O controller) is PPI
Programmable Peripheral Interface (PPI)
Programmable Peripheral Interface (PPI)
CPU PPIParallel
I/O Device Printer
Accessing the Parallel Port Through BIOS Functions
Accessing the Parallel Port Through BIOS Functions
INT 17H Services00 Display Characters01 Initialize Printer 02 Request Printer
DX register
Port Interface Number0=LPT1,1=LPT2,2=LPT3
Accessing the Parallel Port
Through BIOS Functions All the function Return in AH the Current Printer Status
7 6 5 4 3 2 1 0
Printer BusyReceive Mode Selected
Out of Paper
Time out
Transfer ErrorPrinter OffLine
Accessing the Parallel Port
Through BIOS Functions Time Out Byte0040:0078 LPT10040:0079 LPT20040:007A LPT3
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
Importance of the Status Byte
Importance of the Status Byte
If((pstate&0x29)!=0)or ((pstate&0x80)==0) or ((pstate&0x10)==0){printerok=FALSE;}else{printerok=TRUE;}
Importance of the Status Byte
17H/00H Write a character on entry AH=00AL=ASCII code DX=Interface#On exitAH=Status Byte
17H/01H Initialize Printer on entry AH=01DX=Interface#On exitAH=Status Byte
17H/02H Get Printer Status on entry AH=02, DX=Interface# On exit AH=Status Byte
Printing Program
Printing ProgramREGS regs; FILE *fptr;void main(void){fptr=fopen(“c:\\temp\\abc.text”,”rb”);regs.h.ah=1;regs.x.dx=0;int86(0x17,®s,®s);while(!feof(fptr)){regs.h.ah=2;regs.x.dx=0; int86(0x17,®s,®s); if ((regs.h.ah & 0x80)==0x80) { regs.h.ah=0; regs.h.al=getc(fptr); int86(0x17,®s,®s);}}}
#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)();
}
Printing Program 1
#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)();
}
Printing Program 2
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;(*old)();_AH=0;(*old)();
}else
(*old)();}
Printing Program 3
Direct Parallel Port Programming
Direct Parallel Port Programming• BIOS support up
to three parallel ports
• Address of these LPT ports is Stored in BIOS Data Area40:08 word LPT1
40:0A word LPT240:0C word LPT340:0E word LPT4
Direct Parallel Port Programming Dump File Text
Direct Parallel Port Programming
unsigned int far * lpt = (unsigned int far *) 0x00400008 ;unsigned int temp;temp=*(lpt); *lpt=*(lpt + 1);*(lpt + 1)=temp;
Direct Parallel Port ProgrammingPort 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
Printer Data Port
7 6 5 4 3 2 1 0
Base +0 = Data Port
Printer Status RegisterBase + 1 = Printer Status
Busy=0
ACK=0
PE=1
SL=1 ERR=0 0 0 0
Printer OnlineOut of Paper
Printer is ready for Next Character
Printer is Busy
7 6 5 4 3 2 1 0
7 6 5 4 3 2 1 00 0 0 IRQ SI IN ALF ST
Printer Control Register = Base + 2
STROBAuto LineField
initializeIRQ ENABLE
SELECT InLineTurn Computer on line
Printer Control Register
Execute Interrupt When ACK=0;
Direct Parallel Port Programmingfile *fptr;unsigned far *base=(unsigned int far *)0x00400008void 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); }}}