Output to Parallel Port

GENERAL Help
1

Hello,

I am trying to use my parallel port to talk with external hardware (ADC0804). I cannot send simple output to the data-register of the parallel port. Here is the code I am using:

#include <stdio.h>
#include <unistd.h>
#include <stdint.h>
#include <hw/inout.h>
#include <sys/neutrino.h>
#include <sys/mman.h>

#define PORT_LENGTH 1

#define DATA_ADDRESS 0x378
#define CTRL_ADDRESS 0x37a
#define INIT_BIT 0x04
#define LOW 0x00
#define HIGH 0xFF
#define MAX_COUNT 60

int main( )
{
int privity_err,count;
uintptr_t ctrl_handle, data_handle;

privity_err = ThreadCtl( _NTO_TCTL_IO, NULL );
if ( privity_err == -1 )
{
	fprintf( stderr, "can't get root permissions\n" );
	return -1;
}

ctrl_handle = mmap_device_io( PORT_LENGTH, CTRL_ADDRESS );
out8( ctrl_handle, INIT_BIT );

data_handle = mmap_device_io( PORT_LENGTH, DATA_ADDRESS );

for ( count = 0; count < MAX_COUNT; count++ )
{	
	out8( data_handle, LOW );
	printf( "Low\n" );
	sleep( 1 );

	out8( data_handle, HIGH );
	printf( "High\n" );
	sleep( 1 );
}
return 0;

}

For some reason, when I read the voltage on the data-pins with a multimeter, they never change! Can any suggestion a solution?

Thank you.
Matt.

2

I could be wrong, but I think the 0x04 INIT bit you are setting is the Bi-Directional bit. Setting this bit means you want to read data from the cable, not send data to it.

3

I have some success…But wait.
I don’t send any configuration to the port, all i send is out8(0x378,0xaa), and it properly sets the data bits. However, when I add two lines, say

out8(0x378,0xaa);
sleep(1);
out8(0x378,0xff);

nothing happens, the lines remain at 0xaa. I have “slay devc-par” and nothing seems to allow more than one call to the parallel port. any ideas? The status register is always at 0x7F, while the control is always at 0xc6.

4

Please see my other posting on ECP vs. NORMAL, Bi, and EPP.

5

I seem to have better success now that I have changed my port settings in the BIOS. However, the settings are a little confusing. I am using a P3 Compaq 500Hz PC, and within the BIOS, there are a few options, not immediately clear to me. I can change the Onboard Device Options, and the Printer Mode.

In Printer Mode, I have options of (Standard) or (Flexible) or (Output-Only). How do these relate back to SPP, Bi, ECP and EPP???

In Device Options, I can set memory locations, along with DMA settings. These are some examples:
(378-37A, 778-77D, IRQ 9)
(378-37A, 778-77D, IRQ 10)
(378-37A, 778-77D, IRQ 7, DMA 3)
(378-37A, 778-77D, IRQ 9, DMA 3)
Is the DMA only used in EPP mode?

Thanks for any help on this clarification, I cannot find anything on the web.

6

The people who made this computer must be demented. Oh, you mentioned it was Compaq, so that is redundant.

Usually “SPP” which is output-only is called “standard”.
Output-Only should work fine.
I’ll bet their “Standard” is really Bidirectional. The best way to check
is to see if toggling the 5 (0x20) or 7 (0x80) stops output. While some ports use 5, there are some that use 7.

Flexible, who knows? Maybe ECP? Usually with ECP you have to choose a DMA channel. Try writing to and then reading from port base+3.
If you get something back, it is probably EPP. For ECP read at base+ 0x402 and see if you get something other than 0xff.

EPP does not use DMA, but ECP does.

7

It appears that “standard” is the bidirectional state since I am able to input values to the data port when I write 0x20 to the control port, while outputting values when i write 0x00 to the control. One thing however, is that when I do output 0x20 to the port, the port control port gives me the proper behaviour, however, when i read its value, it doesn’t retain the value of 0x20. For example, i wrote 0x20 to the port, and read back 0xe0. Or, I write 0xab and read back 0xeb.

Another quick question. I am trying to interface the parallel port to an ADC, and I was just going to use the Bi-directional mode. Is it much more trouble to use the ECP mode, seing as it can handle much quicker speeds?

8

I think that bit set to output more are not readable (not will not read what you wrote)

9
10

Wow, openqnx.com is not friendly. First I accidentally posted a reply, and next it won’t let me edit it. Snarl.

Well let me be brief this time. The bi-directional parallel port can move data up to about 3MegaBytes per second. A recent modern port should be able to do this. This is pretty darn fast. In ECP mode, you get some benifits. There’s a FIFO buffer, DMA transfers, and RRL expansion if you are reading data. This will no doubt take more work. How much, I don’t know. I’ve never written any ECP code. Frankly I’d rather chew razor blades then figure out hardware designed by the big MS. You may feel otherwise.