Something we want to connect more peripheral module to our computer via parallel port. Traditionally we can multiplex this port with multiplexing IC such of PPI 8255. To establish connection between PPI IC and parallel port we simply use IC buffer, image below show the complete circuit:

2. Before starting program we call this procedure to set PPI8255 operation mode, just like this:

inisialisasi($8B); { control word for A=out, B&C=input }

This Control word make A port as output port and B, C port as input port.

 

3. After sending control word, we can perform write action or read action, to do this we can use an VCL that has been already such of small port. It is will shortening our work.

We must understand that in this circuit, data that being readlnis in nible format, so if we send 8 bit data, we must receive in two step consequencially. Below is example for reading data that being sent via B port:

edit1.text := hexa((InpB shr 4) and $0F) + hexa(InpB and $0F) + ‘ H’;

Data from B port will readln and display it in edit1 component.

And Instruction in program code above is to perform masking operation with $0F

Also in this code, we use a procedure called InpB procedure .InpB procedure performing read action on B port.

Below is program listing for InpB procedure :functionTForm1.InpB:byte;

var tmp : byte;

begin

smallport1.WriteByte(LPT_kontrol,$00);//ready for read 0000, 574 out become -off

smallport1.WriteByte(LPT_data,$E5);//RD = low 1110 0101, read from port B

smallport1.WriteByte(LPT_kontrol,$08);//1000,incoming data fromA to Y 74LS157

smallport1.WriteByte(LPT_kontrol,$00);//0000

tmp := smallport1.ReadByte(LPT_status) xor $80; //xor for inversstrobe

tmp := (tmp shr 4) and $0F;

smallport1.WriteByte(LPT_kontrol,$04); //0100, incoming data fromB to Y

InpB := tmp or ((smallport1.ReadByte(LPT_status)xor $80) and $F0);

end;

4. You can get full tutorial code ( In Delphi) via this link. The program performing read action on B and C port, but it easily to make another function like writing A port .