[PARPORT] reading data from the parport?

Clemens Kirchgatterer (clemens@root.at)
Wed, 05 May 1999 17:44:11 +0200

hi there!

im trying to connect a OTREX grafix_lcd-panel to the parallel port, but
ran into some problems.

i have to read the lcd status from the data lines bovor i can write (or
read) data and commands to the panel, but
everytime i read the PORT_BASE+0 i get the last written byte back.

code tells more:

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <asm/io.h>

#define PORT_BASE 0x378

#define PORT_READ outb((inb(PORT_CTRL) | 0x20), PORT_CTRL)
#define PORT_WRITE outb((inb(PORT_CTRL) & 0xdf), PORT_CTRL)

void lcd_write_data(data) {
  PORT_WRITE; //clear bit 5 of parport
control register to enable writing
  outb(data, PORT_DATA);

int lcd_read_data(void) {
  PORT_READ; //set bit 5 of parport
control register to enable reading
  return (inb(PORT_DATA));

main(void) {
  if (ioperm(PORT_BASE, 3, 1)) {perror("IO ERROR parallel-port");

  printf("Setting Data-Lines to 0xff ...\n");
  printf("Reading Data-Lines ... ");
  printf("%d\n", lcd_read_data());
  printf("Setting Data-Lines to 0x00 ...\n");
  printf("Reading Data-Lines ... ");
  printf("%d\n", lcd_read_data());

i have activated EPP-Mode in the BIOS setup, so everthing should be OK.

any suggestions?

warm regards


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This archive was generated by hypermail 2.0b3 on Wed 05 May 1999 - 11:45:20 EDT