[N8VEM: 17953] SBC-188 up and running.... Sort of.

Discussion:

Edward Snider

2014-04-27 23:19:53 UTC

Hi Everyone,

I've been trying to get my SBC-188 v2 up and running.

It seems to be working ok, but only if I pull U17 and U25.
The only thing going to these chips are address lines and the BUSAK signal.

With these sockets empty, it posts, clock works, and I get all the way to
the BASIC interpreter,
which seems to run fine with a few simple programs I keyed in (I have not
hooked up a drive yet).
With these 244's in, no post, serial output, nothing but a lit (halt/ halt)
led.

All logic is LS. I noticed some posts seeming to indicate that the
microprocessor is able to sink only a very limited
amount of current on the address lines (I have the AMD version), and that
lower power logic substitutions have helped some
situations. Does this sound like it is likely the issue?

I'm going to get some other logic to try for the 373's and 245 to see if
this helps.

Any thoughts?

Thanks,

Ed

--
You received this message because you are subscribed to the Google Groups "N8VEM" group.
To unsubscribe from this group and stop receiving emails from it, send an email to n8vem+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/***@public.gmane.org
To post to this group, send email to n8vem-/JYPxA39Uh5TLH3MbocFF+G/***@public.gmane.org
Visit this group at http://groups.google.com/group/n8vem.
For more options, visit https://groups.google.com/d/optout.

John Coffman

2014-04-28 02:33:58 UTC

Permalink

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta content="text/html; charset=ISO-8859-1"
http-equiv="Content-Type">
<title></title>
</head>
<body bgcolor="#ffffff" text="#000000">
On 04/27/2014 04:19 PM, Edward Snider wrote:
<blockquote
cite="mid:15f47ccb-e4a2-48f7-8852-22db0a02c37d-/***@public.gmane.org"
type="cite">
<div dir="ltr">Hi Everyone,
<div><br>
</div>
<div>I've been trying to get my SBC-188 v2 up and running.  </div>
<div><br>
</div>
<div>It seems to be working ok, but only if I pull U17 and U25.</div>
<div>The only thing going to these chips are address lines and
the BUSAK signal.<br>
</div>
</div>
</blockquote>
<br>
The outputs from the 80C188 supposedly can sink 2ma, if I remember
the data sheet correctly.  This is an LS fanout of 5.  Any potential
overload would be on AD0..AD7.  U4 (LS374) is the first chip to
convert to ALS374. <br>
<br>
Voltage problems on the board may be more of a concern.  Depending
upon whether you are powering the board from the DIN connector
plugged into a backplane, or from the Molex connector, check the Vcc
on several chips around the board.  It should be as close to +5.00v
as possible.  Also any differential in GND potential from where
ground is connected to the board.  GND is probably less of a
problem, since the copper fill areas top and bottom are connected to
GND.  But Vcc is routed around the board, and if there is not enough
solder in some hole that it is routed through, you may have a
voltage drop.<br>
<br>
Is the serial chip (16C550) a CMOS chip?  Check all the chips that
connect to the ADx lines.  They should present minimal loading on
those lines.<br>
<br>
--John<br>
<br>
<br>
</body>
</html>

<p></p>

-- <br />
You received this message because you are subscribed to the Google Groups "N8VEM" group.<br />
To unsubscribe from this group and stop receiving emails from it, send an email to <a href="mailto:n8vem+unsubscribe-/***@public.gmane.org">n8vem+unsubscribe-/***@public.gmane.org</a>.<br />
To post to this group, send email to <a href="mailto:n8vem-/***@public.gmane.org">n8vem-/***@public.gmane.org</a>.<br />
Visit this group at <a href="http://groups.google.com/group/n8vem">http://groups.google.com/group/n8vem</a>.<br />
For more options, visit <a href="https://groups.google.com/d/optout">https://groups.google.com/d/optout</a>.<br />

Edward Snider

2014-04-28 16:35:30 UTC

Permalink

Thanks John, I will check those voltages out. Yes, the uart is CMOS.

I'm ordering some ALS and HCT chips to try out, all I have on hand is LS
right now.

Ed

Post by Edward Snider
Hi Everyone,
I've been trying to get my SBC-188 v2 up and running.
It seems to be working ok, but only if I pull U17 and U25.
The only thing going to these chips are address lines and the BUSAK signal.
The outputs from the 80C188 supposedly can sink 2ma, if I remember the
data sheet correctly. This is an LS fanout of 5. Any potential overload
would be on AD0..AD7. U4 (LS374) is the first chip to convert to ALS374.
Voltage problems on the board may be more of a concern. Depending upon
whether you are powering the board from the DIN connector plugged into a
backplane, or from the Molex connector, check the Vcc on several chips
around the board. It should be as close to +5.00v as possible. Also any
differential in GND potential from where ground is connected to the board.
GND is probably less of a problem, since the copper fill areas top and
bottom are connected to GND. But Vcc is routed around the board, and if
there is not enough solder in some hole that it is routed through, you may
have a voltage drop.
Is the serial chip (16C550) a CMOS chip? Check all the chips that connect
to the ADx lines. They should present minimal loading on those lines.
--John

Edward Snider

2014-07-12 22:02:46 UTC

Permalink

Finally got back around to trying to debug this board. Apparently there
*was* some overloading of the
address lines. Replacing the LS373's and LS244's with ALS logic was enough
to solve the problem.

Seems to work fine now. :)

Ed

Post by Edward Snider
Thanks John, I will check those voltages out. Yes, the uart is CMOS.
I'm ordering some ALS and HCT chips to try out, all I have on hand is LS
right now.
Ed

Post by Edward Snider
Hi Everyone,
I've been trying to get my SBC-188 v2 up and running.
It seems to be working ok, but only if I pull U17 and U25.
The only thing going to these chips are address lines and the BUSAK signal.
The outputs from the 80C188 supposedly can sink 2ma, if I remember the
data sheet correctly. This is an LS fanout of 5. Any potential overload
would be on AD0..AD7. U4 (LS374) is the first chip to convert to ALS374.
Voltage problems on the board may be more of a concern. Depending upon
whether you are powering the board from the DIN connector plugged into a
backplane, or from the Molex connector, check the Vcc on several chips
around the board. It should be as close to +5.00v as possible. Also any
differential in GND potential from where ground is connected to the board.
GND is probably less of a problem, since the copper fill areas top and
bottom are connected to GND. But Vcc is routed around the board, and if
there is not enough solder in some hole that it is routed through, you may
have a voltage drop.
Is the serial chip (16C550) a CMOS chip? Check all the chips that
connect to the ADx lines. They should present minimal loading on those
lines.
--John