On Tue, May 11, 2004 at 08:44:20AM -0800, Dave Baldwin enlightened us
thusly
> > I must be getting to be a real pain at this stage, Dave, and thanks
> > for taking me through this.
>
> No problem.
>
> > > A minor point but a number of microprocessors don't go to 0x0000
> > > hex at reset. Reset vectors in some cases are in the 0xFF00 hex
> > > page and I believe the Motorola 68xx and the Hitachi 63xx are
> > > among those. Come to think of it, I believe that x86 reset goes
> > > to 0xFFFF00 hex to get it's first instruction after a reset.
> >
> > 1. Output a start signal on a presettable address (from the address
> > bus). Often this would be 0x0000h 2. Given this start signal, output
> > a stop on a clock count. 3. Alternatively, stop on another address.
> > 4. Probably an optional reset signal just after the stop would be
> > nice to get another sample. Saves farting with a watchdog, and works
> > when there isn't such a device on the board.
> >
> > All of this is probably do-able from 1 Eprom clip on the board for
> > boards with an eprom. After that, it gets messy here due to the
> > range of uPs I meet (80xx, 8088, 8085, Z80, TMS7000, PICs, ATMELs,
> > HD64xxxx, 68xx, & 65xx being the common ones)
>
> Of the micros listed, the only ones that I know go to 0x0000 hex on
> reset are the 8085 and the Z80. 8031/51 and HD64180 too. The 68xx
> and the 65xx don't necessarily ever go to 0x0000 hex as far as I know.
The HD64180 is not a problem. I do meet the HD647586, or summat (None
here now). I imagine most of them will read bytes addressable by the
address bus. I imagine that they will be sent low if they don't go there
automatically; after all, they count up, don't they? And the uP support
devicxe addresses might be just as useful as the 0000. In fact, there is
no particular advantage in that one at all.
>
> HP used to make a scope that used a pair of 8-bit DACs, one for the
> horizontal and one for the vertical, to display address patterns on
> the screen. I think the DAC's were loaded on the memory control
> signals RD and/or WR so the display wasn't just a bunch of fuzz. This
> works pretty good if you have a known good unit to compare the unit
> under test to.
Actually, that is not much use. Repair houses rarely have good pcbs -
only crap. What is needed is to record the patterns of a good board, and
store them for future use. Hence the DSA(Digital Signature Analyser),
with it's checksums, and the ASA (Analogue Signature Analyser) with it's
recordable signatures are useful tools. The ASA without recording is
very ordinary as a piece of testgear.
There is actually a very nifty and useful piece of testgear coming
together in my head out of all of this. A proper business idea, even.
But I can't handle the software end.
--
With best Regards,
Declan Moriarty.
--
Author: Declan Moriarty
INET: [EMAIL PROTECTED]
Fat City Hosting, San Diego, California -- http://www.fatcity.com
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