GeForce, G4

2
>kayser@... wrote:
>
> >
> > Other question: I would like to trigger the stimulus presentation
> > from outside using a TTL +-5V signal. What's an easy way to do
> > this on a G4: Serial port, USB, FireWire etc.?
>
>TTL logic levels are +5 and 0 volts, not +-5V. (And only nominally, real
>TTL ( LS, F, AS etc. families) does not swing to the poles, though the HC
>and HCT stuff does).
>
>Neither Serial, USB, nor FireWire ports provide a TTL output directly. You
>can attach to those ports devices which provide parallel digital inputs and
>outputs. One such device is this:
>http://www.activewireinc.com/

The serial ports do provide binary signals (handshaking control lines)
and at least one of these (CTS) may be written from the SERIAL MEX
file (Mac version at least, not sure about Windows). Although the
output levels are not TTL, it is pretty easy to build a little circuit
that converts what you do get to TTL -- probably one transistor
or op amp is enough, along with a 5 volt power supply.

DB
3
David Brainard wrote:

> >kayser@... wrote:
> >
> > >
> > > Other question: I would like to trigger the stimulus presentation
> > > from outside using a TTL +-5V signal. What's an easy way to do
> > > this on a G4: Serial port, USB, FireWire etc.?
> >
> >TTL logic levels are +5 and 0 volts, not +-5V. (And only nominally, real
> >TTL ( LS, F, AS etc. families) does not swing to the poles, though the HC
> >and HCT stuff does).
> >
> >Neither Serial, USB, nor FireWire ports provide a TTL output directly. You
> >can attach to those ports devices which provide parallel digital inputs and
> >outputs. One such device is this:
> >http://www.activewireinc.com/
>
> The serial ports do provide binary signals (handshaking control lines)
> and at least one of these (CTS) may be written from the SERIAL MEX
> file (Mac version at least, not sure about Windows). Although the
> output levels are not TTL, it is pretty easy to build a little circuit
> that converts what you do get to TTL -- probably one transistor
> or op amp is enough, along with a 5 volt power supply.

Some added advice to David's comments on using the Serial port CTS pin for
digital output:
- If you are using a new Mac which does not have serial ports, then you will
have to add a serial port either using a PCI card or one of the USB/Serial port
Adapters.
-You can get in one chip a circuit which converts between RS232 voltage levels
and TTL levels, and it's powered by a +5V supply. I think they are usually
called "rs232 transceivers." I don't have a part number handy, but you could
probably find one in the digi-key catalog, which is available online.
Manufacturers have their spec. sheets available online in PDF format now, so it
should be easy to track one down and get the specs.

Allen