[Info-vax] [OT] Serial ports as GPIO devices, was: Re: OpenVMS 5.5 shared folder on a windows network ?

[Simon Clubley]

On 2010-07-29, John Wallace <johnwallace4 at yahoo.co.uk> wrote:
>
> The fact that parallel printer ports weren't designed to do simple
> digital IO hasn't stopped them being used for it quite extensively in
> the world of low-cost electronic interfaces. In some of those cases,
> in a modern PC the parallel port chip (or its SuperIO replacement)
> simply isn't there for some vendor's custom driver to talk to. There's
> no way that kind of hardware change from parallel to USB can be fixed
> without heartache of some kind, however much good work various good
> folks may have done for USB printers.
>

The control lines on the serial port can also be used for this.

At home, I am using a AVR programming circuit which is attached to the
serial port control lines and the programmer uses those control lines
to implement the AVR programming protocol.

There's no way you could do that on a USB serial port with the latency
involved.

BTW, the circuit is linked to from this page if you are interested:

http://olimex.com/dev/avr-pg1.html

Simon.

-- 
Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
Microsoft: Bringing you 1980's technology to a 21st century world