IEEE-488 cart (was Re: D9090 (was Re: VIC-1001 ROM sighting))

From: Ethan Dicks (
Date: 2001-09-19 16:45:07

--- Ruud Baltissen <> wrote:
> Hallo Daniele, Ethan,
> ...mine had a pair of TI IEEE-488 line-driver chips, the C= VIC-20 IEEE cart
> had three (MC3446)
> The pair of TI-IC's you mention are hard to get and rather expensive.

No doubt.  For interfaces, though, the right chip is still the right chip.
I'm living through that with DEC OMNIBUS and Qbus interfaces.  I really need
an 8837 right now to fix a Heathkit floppy controller.  I'd trade a tube
of what I have (things like DS8641s) for a small handful of 8837s.

> On the other hand the MC3446 can be replaced by a 7407 (not pin 
> compatible !!!).

But how are the specs?  It's an easy-to-get chip, but is it _really_ 
a replacement, or is it just close?  I know I have specs on the 7407.
I don't think I do for the MC3446 (I might, if they are buried inside
one of the CBM drive technical manuals).

> The input of the 6522 now serves as input. 

Do you mean that the 6522 is hooked right to the GPIB without any buffering?
If so, then you are probably limited to one or two peripherals.

> The disadvantage of this
> construction is that the moment you switch off the device, you may
> experience trouble with the communication between other devices.

Since we are probably talking about adding a GPIB to a CPU, unless you
happen to have a disk->print spooler or a 4040->8250 autonomous copy
going on, I don't see a problem with that.  If, OTOH, one considers
using this for a modern D9090 emulator (getting back to the original
topic) or perhaps a PC-based disk simulator, then it might be an issue.


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