25 Dec
2002
25 Dec
'02
5:22 p.m.
So I'm using the holiday pause to hopefully get my project to build an
interface for my Documation M200 card reader back on track.
I'm using an Apple ][ with a serial card and custom 6522 VIA card as a
parallel to serial converter. The 6522 has just enough inputs to read all
data and signal lines from the reader.
The documenation from the reader is online thanks to David Gesswein. It
has been very helpful, but proves to be too cryptic for this novice to be
able to build the connector. I have the ELCO connector almost all wired
up. The last step is to get the wiring between the cable and the 6522
VIA connector bridge that I've built.
The manual says the output is a "type 7404 TTL output" and a diagram in
the same shows some voltages and current draws that make no sense to me
and don't really facilitate an understanding (at least to this untrained
eye) of what to expect on the pins as data is read.
26 Dec
26 Dec
7:38 a.m.
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11:04 a.m.
On Thu, 26 Dec 2002, Tony Duell wrote:
The first confusion is to whether it's a 7404
output (as specified here)
or a 7416 output (as shown in the diagram). The main difference to you is
that the '16 is an open-collector device. If it's that, you need to wire
a pull-up resistor (1k or so) between the output signal line and a +5V
supply (take that from the Apple). If it's a '04, then you don't need
these resistors.
That is indeed one main element of my confusion. Why do simple errors
like this make it past the technical writers?
How do I know for sure which to use? Is there some way I can check with a
simple volt meter or something?
IIRC, the 'return' pins are just grounds.
They're all linked together
inside the reader, and linked to the reader's 0V rail. The idea is to use
twided pair cable, one wire for the signal, one for the return. On
short-ish cable runs you shouldn't need to do this -- just wire up some
of the 'return' wires to ground at the Apple end.
Ok, this is also what John Lawson instructed, which makes sense. My cable
is less than 10ft long (about 3m).
The M200 has a fair amount of electronics in it, and I
can assure you
that the outputs come from logic ICs, not from mechanical contacts. You
don't need optoisolators.
This is the opposite of what John tells me. You're both highly competent.
To whom shall I defer?
(I would prefer to defer to you because it means far less work for me ;)
Sellam Ismail Vintage Computer Festival
------------------------------------------------------------------------------
International Man of Intrigue and Danger http://www.vintage.org
* Old computing resources for business and academia at www.VintageTech.com *
11:16 a.m.
On Thu, 26 Dec 2002, Sellam Ismail wrote:
You can always trace back the data lines inside the reader, to see if they
run to mechanical contacts or some sort of semiconductors. Just be
careful that you don't generate a ground loop if the ground on the reader
and the Apple are at different voltage levels and somehow associated -
like something on the lo-v side of the power supply connected to earth
ground.
Pat
--
Purdue Universtiy ITAP/RCS
Information Technology at Purdue
Research Computing and Storage
http://www-rcd.cc.purdue.edu
On Thu, 26 Dec 2002, Tony Duell wrote:
You should be able to tell... check if it gives a close to +5V output for
a high signal (relative to the 'return line') with, say, a 470ohm
resistor to ground. you may also want to check that it gives a close to
0V output for a low signal If so, you don't need the pullup resistors.
The first confusion is to whether it's a 7404
output (as specified here)
or a 7416 output (as shown in the diagram). The main difference to you is
that the '16 is an open-collector device. If it's that, you need to wire
a pull-up resistor (1k or so) between the output signal line and a +5V
supply (take that from the Apple). If it's a '04, then you don't need
these resistors.
That is indeed one main element of my confusion. Why do simple errors
like this make it past the technical writers?
How do I know for sure which to use? Is there some way I can check with a
simple volt meter or something? The M200 has a
fair amount of electronics in it, and I can assure you
that the outputs come from logic ICs, not from mechanical contacts. You
don't need optoisolators.
This is the opposite of what John tells me. You're both highly competent.
To whom shall I defer? 
11:22 a.m.
New subject: Documation - Apple I/O
Just to take the "opto / no opto" discussion public.. in respect of
connecting the Documation TTL outputs to the TTL inputs of an Apple VIA
card in an Apple ][ ...
I respectfully beg to disagree with my Learned Friend Dr. Duell. As I
privately wrote to Sellam, I am afraid of (and have been badly bitten by)
directly interfacing dissimilar machines, and then encountering
poorly-designed power supplies that 'hunt' and attempt to regulate each
other over the logic lines, with occasionally spectacular results.
Wiring up a couple of octal or hex optoisolators should take a two hours
max, and then no worries, Moit!
I am just trying to err on the side of caution. Were it me, with my
resources and equipment, I'd just measure between the devices to make sure
no VooDoo was lying in wait, then go ahead and splice the cables. In
Sellam's case, he does not have rooms full of sophisticated test gear, and
so I thought isolating the signals would serve to protect the machines,
especially the card reader I/O circuits.
Your Milage May Vary, as they say.
Cheers
John
12:30 p.m.
New subject: Documation - Apple I/O
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12:03 p.m.
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