12-31-2008 05:48 AM
Why can't my 74hc373 not drive even a 100k load?
(I'm doing my best just to ask my question and keep my composure, for I've been down this Multisim+new=Multisim-bug route before. In other words, the attached circuit should have the necessary components to field my question.)
The idea is to pass the high at the d-input to the q-output given a high enable via the switch closure. I'm seeing the q-output go high (3v) with the switch, unless I attach a load of anything (reasonable things I could think of) but a voltmeter. Using the voltmeter, it seems the q-output will not go to anything higher than 60mV when a load is attached. Since when can an HC output not drive a load of anything but a voltmeter?!
This looks like a digital component error on Multisim's part, but maybe it's my error in some way I'd not considered (in the Multisim world.)
I believe the key to solving this problem is to get the q-output to be high with a load (besides a voltmeter, scope, "probe" etc.)
Any takers?
12-31-2008 05:54 AM
12-31-2008 06:07 AM
As I couldn't figure out how to edit my first post to add to it, I'm attaching this to it:
Incidentally, I just tried the LS version of the 373, and it can't drive a load either.
The next thing to try is a gate. ...I bet it'll drive a gate but not an actual (in the Multisim world) component...
12-31-2008 12:57 PM
Hi there,
This behaviour that you've described is a problem specific to Multisim 10.1. Fortunately, we have fixed it already and it will be distributed with our update for 10.1. This update will come out early next year so stay tuned!
I can't think of a work around for this right away, but if anyone does, please let us know.
12-31-2008 09:44 PM
Thanks. I'm glad the problem has been addressed in the next version, as I don't often do such mixed simulation, but on occasions such as this one I'll need to.
In the meantime, as I know for a fact it's a bug now, I can maybe piece something together for a work-around. If I get something, I'll come back and give a heads up.
It stinks that it seems the only time I really have time (actually I have to make it) to come here is when I have a problem, but I'm so glad this forum exists.
Once again, thanks.
01-02-2009 09:33 AM
If you don't need to place the output of this circuit in high impedance (i.e. ~OE is permenantly tied to GND), you can place a voltage buffer on the output of each pin for simulation purposes. You can get such a buffer with a VOLTAGE_CONTROLLED_VOLTAGE_SOURCE with a gain of 1.
If you need tristate functionality, it would be more complex, but I would imagine that you could obtain high impedance behaviour with the use of a few switches.