B&B Electronics Parallel Printer Card PIOC Manuale Utente Scaricare il pdf (Pagina 6)

Interfacing the Standard Parallel Port http://www.senet.com.au/~cpeacock

Interfacing the Standard Parallel Port Page 6

The above table, table 3, shows the address at which we can find the Printer Port's addresses in

the BIOS Data Area. Each address will take up 2 bytes. The following sample program in C, shows

how you can read these locations to obtain the addresses of your printer ports.

#include <stdio.h>

#include <dos.h>

void main(void)

{

unsigned int far *ptraddr; /* Pointer to location of Port Addresses */

unsigned int address; /* Address of Port */

int a;

ptraddr=(unsigned int far *)0x00000408;

for (a = 0; a < 3; a++)

{

address = *ptraddr;

if (address == 0)

printf("No port found for LPT%d \n",a+1);

else

printf("Address assigned to LPT%d is %Xh\n",a+1,address);

*ptraddr++;

}

Software Registers - Standard Parallel Port (SPP)

Offset Name Read/Write Bit No. Properties

Base + 0 Data Port Write (Note-1) Bit 7 Data 7 (Pin 9)

Bit 6 Data 6 (Pin 8)

Bit 5 Data 5 (Pin 7)

Bit 4 Data 4 (Pin 6)

Bit 3 Data 3 (Pin 5)

Bit 2 Data 2 (Pin 4)

Bit 1 Data 1 (Pin 3)

Bit 0 Data 0 (Pin 2)

Table 4 Data Port

Note 1 : If the Port is bi-directional then Read and Write Operations can be performed on the Data

The base address, usually called the Data Port or Data Register is simply used for outputting

data on the Parallel Port's data lines (Pins 2-9). This register is normally a write only port. If you read

from the port, you should get the last byte sent. However if your port is bi-directional, you can receive

data on this address. See Bi-directional Ports for more detail.

1 2 3 4 5 6 7 8 9 10 11 ... 16 17

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B&B Electronics Parallel Printer Card PIOC Manuale Utente Pagina 6