Standard serial/parallel ports for new PC

[Lennart Sorensen]

On Sun, Jan 20, 2008 at 11:30:57PM -0500, Kevin Cozens wrote:
> The one thing my new computer (HP computer with Core 2 Duo processor) 
> doesn't have is either a serial or parallel port. I know there are USB 
> adapters to provide these types of ports but they aren't useful to me. I 
> have some programs which require being able to do bit-bashing on the ports. 
> I also want to do use the parallel port for interfacing with some 
> electronic circuits, and I can use it with my old laser printer.

What do you actually want to be able to do with the ports?

> I would like to get a single board that has a 9-pin serial port compatible 
> with a standard 8250/16450/16550 chip, and a 25-pin parallel port 
> compatible with a standard 8255 chip, and that use standard IRQ's for each 
> of the serial and parallel ports on the board.
> 
> The boards I have found are a in the $60 to close to $100 but seem to share 
> a single IRQ. Since they do that, I would question their compatability with 
> the ports found on older computers. Anyone happen to know of a source for 
> such a board? If I can't get both ports on one board, I could go with just 
> a parallel port board for now.

PCI devices will share an IRQ since that's what PCI does and since there
is no reason not to.  Since they are level triggered rather than edge
triggered (like ISA was) then sharing is no problem.

> The board(s) need to be Linux compatible. A board that would work but comes 
> with some custom Windows driver isn't likely to be useful. The alternative 
> would be to make one myself but that is likely to be a hassle to interface 
> with the PCI bus used in the current day machines.

Well a USB parallel port should be pretty standard and should look
excactly the same to user space as a built in one, so you can bitbang
through the /dev/parport# interface whatever you want.  The parport
device is certainly generic and low level enough that there can't be any
reason you should ever want to access the port registers directly.

As for serial, there are certainly a number of USB serial ports that
work with linux just fine.

PCI cards also work for both and they should in general be 16550
compatible for the serial and PCI parallel compatible for the parports.
Some are different (like the Digi Neo 2 port serial card) which has an
Exar uart with a 64byte FIFO which uses the 'jsm' driver in linux, but
works amazingly well, but sure isn't a 16550.

--
Len Sorensen
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