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From: D Yuniskis on 18 Jan 2010 18:16
Rowan Sylvester-Bradley wrote:
> I have to create a test harness to allow automatic testing of a system
> that I'm working on. It needs several hundred digital inputs and several
> hundred digital outputs. They don't need to be isolated or anything -
> just logic input/outputs. I don't mind much what it looks like or what
> the form factor is, or how it interfaces to the PC (USB, PCI, ISA etc.)
> - I just want to minimise the cost. Can anyone suggest the lowest cost
> way of adding a lot of digital I/O to a PC?

Nowadays, I wold opt for tying into an IDE card to get off the
bus and into "user land". No, don't create a "disk device"
but, rather, just write to those I/O ports and hang your
device off that 40pin ribbon.

Printer ports are going away (gone?).

IDE is as well -- but you can still find PCI IDE cards.
A tiny bit of steering logic and a kludgey protocol
to talk to the IDE addresses should be a weekend project.

Supporting it on ________ operating system will be the bigger
problem (you may be best served by using an open source "DOS"
and dedicating that machine to that purpose.
From: Uniden on 18 Jan 2010 18:15
In article <ZaY4n.1889$SJ7.1470(a)newsfe07.iad>, rowan(a)sylvester-
bradley.org says...
> I have to create a test harness to allow automatic testing of a system that
> I'm working on. It needs several hundred digital inputs and several hundred
> digital outputs. They don't need to be isolated or anything - just logic
> input/outputs. I don't mind much what it looks like or what the form factor
> is, or how it interfaces to the PC (USB, PCI, ISA etc.) - I just want to
> minimise the cost. Can anyone suggest the lowest cost way of adding a lot of
> digital I/O to a PC?
>
> Thanks - Rowan

USBmicro.com USB to SPI devices connected to a lot of shift registers.
Chips like the 74HC595 and 74HC165. The SPI devices connect in seties
and banks of them can be selected with different chip selects.

The device also interfaces to I2C (and LCD, stepper motor, 1-wire
devices) and is for sale here: circuitgizmos.com
From: -jg on 18 Jan 2010 18:49
On Jan 19, 1:02 am, "Rowan Sylvester-Bradley" <ro...(a)sylvester-
bradley.org> wrote:
> I have to create a test harness to allow automatic testing of a system that
> I'm working on. It needs several hundred digital inputs and several hundred
> digital outputs. They don't need to be isolated or anything - just logic
> input/outputs. I don't mind much what it looks like or what the form factor
> is, or how it interfaces to the PC (USB, PCI, ISA etc.) - I just want to
> minimise the cost. Can anyone suggest the lowest cost way of adding a lot of
> digital I/O to a PC?
>
> Thanks - Rowan

You forgot to mention
a) The R/W bandwidth needed
b) The physical separation of the nodes, and the physical grouping.

A simple and effective expansion, is a serial port in a 'twisted ring'
loop. The master sends with the 9th (parity bit) set 99% of the time,
and the slaves look for a parity-rise, and then remove XX bytes, and
echo XX bytes with the parity cleared, else they simply echo.
As you propagate around the loop, parity-low widens, and you can
insert/remove nodes and they self-locate.

If you need more bandwidth, then flip to something like a FT2232H in
SPI/JTAG mode, and use a chained SPI block.

This can be HCMOS, or CPLD, with CPLD being more flexible.

-jg
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