From: urjlew@ecsvax.uncecs.edu (Rostyk Lewyckyj)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: A4000 Hardware questions
Date: 12 Oct 92 17:16:57 GMT
Organization: UNC Educational Computing Service

In article <35768@cbmvax.commodore.com>, grr@cbmvax.commodore.com (George Robbins) writes:
> In article <1992Oct11.142040.6304@ecsvax.uncecs.edu> urjlew@ecsvax.uncecs.edu (Rostyk Lewyckyj) writes:
> > In article <1992Oct10.192643.7005@TorreyPinesCA.ncr.com>, jgrimm@TorreyPinesCA.ncr.com (Jeffrey Grimmett 9999) writes:
> > > >> 
> > > >> I assume the A4000 still uses the 8520's.  Are there any plans to fold
> > > >> the functionaliy of these into a CMOS ASIC design?
> > > >
> > > 
> > > I wouldn't recommend doing it until something is done about Human Error,
> > > ie folks blowing CIA's sky-high when plugging modems/printers into live
> > > circuits.  I know of and work on several systems which do NOT have this
> > > problem, so I know it's possible.  So, puh-LEEZE take care of that little
> > 
> > I am under the strong impression that a part of the RS232c standard
> > is a statement that it is supposed to be safe to plug and unplug
> > from the circuit while it is live. So the decision by C= to not
> > protect the expensive chips behind the ports from damage in case oc
> > inadverant pin shorting or mildly out of spec signals is poor
> > engineering design. So that the engineers involved don't feel
> > personally insulted, I will blame the decision on corporate chintz
> > rather than their lack of skill or forethought.
> 
> The problem has little to do with the RS232 standard and more to do with
> the printer port and floppy and IBM's wretched choice of using DB25's
> for both serial and parallel ports.
George, I can't understand how IBM's poor choice of using DB25 
connectors for both serial and parallel ports has anything to do
with whether the circuitry behind these ports is or is not protected
on C= Amigas.
C= could certainly have chosen to use the parallel type connector.
They did not hesitate to choose a 23 pin (uncommon) connector 
Don't pass the buck.
> 
> In the original A1000 design, the 8520's had their outputs directly
> wired to the I/O connectors.  This isn't very rugged, but is the most
> flexible as far as supporting both input and output, especially for
> ad-hoc peripherals that use the parallel data lines for random bit
> I/O control/status signals.
> 
> Theoretically, 8520's were cheap and easily replacable, but in the
Whose theory and definitions are these? What is the current cost and
availability of the 8520 chips? $.50-$1.00 from multiple sources?
THe chips protecting the cia should be cheap and socketed. 
CHeap in practice not just in theory.
> systems where they are surface mounted, we have added some protection
> circuitry on the most frequently blown pins.
> 
> We zapped a pile of 8520's trying to determine what kinds of things
> caused failures and what could actually prevent the failures.  Still,
> the best advice is to make sure that your Amiga and parallel printer
> are turned off (or unplugged) before plugging in the parallel port
> cable and don't plug an RS232 cable (+/- 12 volts) in the parallel
> port (+5 volts).  Touch metal on the connector to metal on the system
> before jabbing in the connector to minimize any static charges or
> ground potential differences.
> 
Of course with the system engineered as it is, one needs to take all
possible precautions. Anyone who doesn't is being foolish.
> -- 
> George Robbins - now working for,     work:   to be avoided at all costs...
> but no way officially representing:   uucp:   {uunet|pyramid|rutgers}!cbmvax!grr
> Commodore, Engineering Department     domain: grr@cbmvax.commodore.com