"David Williams" North Star Horizon Help

From: Doug Coward <dcoward_at_pressstart.com>
Date: Fri Oct 9 15:43:38 1998

RE: "David Williams" North Star Horizon Help

 I keep meaning to write up a Horizon troubleshooting guide because
it seem that someone has these same problems about every 6 months.
But I can't even seem to find the time to sit down and just design a
logo graphic for my museum.
 OK here is a quick shoot at it.

>Ok, I have a few minutes now to play around with the N* Horizon
>I've been fixing up. I've tried to power it up and it seems to hit the
>disk drive and then nothing.

Good, if the drive light is coming on that saves some steps.
On a normal load the drive light should be on for about 12 seconds.
The first step would be to see if you are getting a READ error on
the drive.
 1. According to the MDS-A-D controller manual you can test for
a read error at location 7C pin 6. This is the DI-GATE line and
on a read error there will be a continuous stream of pulses on
this line. This chip is 7 columns from the left side and 3 rows
from the top and should be a 74LS00. I tried this out this
morning. I could'nt find my logic probe so I used a voltmeter.
With NO disk error 7C pin 6 stayed at 4.55 VDC. With a disk
error this pin dropped to 1.91 VDC indicating pulses.
 If you are getting disk errors, it could be:
* a blank or bad disk
* a single density disk
* a faulty disk drive
* or a fault in the read circuit of the controller.
Also check that the head carriage guide is in the spiral groove
on the stepper motor cam of the disk drive.

 If you are not getting a disk error then it's narrowed down
to a unpersonalized disk or serial communcations problems.

2. It would help for the next step to have a bus monitor card.
These are like gold if you are dealing with S-100 bus systems
on a regular basis. But you can also just use a bus extender
card to allow you to get to the bus signals with your voltmeter.
 This morning I looked at the address bus after booting with
a working DOS disk and with a unpersonalized DOS disk. With
the standard version that loads at $2000, the I/O routines
are normally placed at $2900-$2A00. The unpersonalized DOS
has it I/O vectors pointing to themself like this:

  $200D C30D20 COUT JMP COUT THIS IS THE CHARACTER OUTPUT ROUTINE
  * Character must be in the B register. Device # may be in the ACC, if
  * desired. On return the character must also be in the ACC. No other
  * registers can be modified. Your routine must do a RET.
  *
  $2010 C31020 CIN JMP CIN THIS IS THE CHARACTER INPUT ROUTINE
  * Device # may be in the ACC, if desired. The 7 bit ascii code must be
  * returned in the ACC. No other registers can be modified. Your routine
  * must do a RET.
  *
  $2013 C31320 TINIT JMP TINIT THIS IS THE TERMINAL INIT ROUTINE
  * All registers can be used. If not needed, point to a RET.
  *
  $2016 C31620 CONC JMP CONC THIS IS THE CONTROL C DETECTION ROUTINE
  * Returns Z set if control C is typed, else returns Z cleared if other
  * character or no character is typed. All registers can be used.

In both cases bit 13 of the address bus is alway active ($2000).
With the unpersonalized disk the 8 lower bits were the ONLY other
active lines. But with the working disk, bits 8-11 were also active.
So, checking address bits 8-11 for activity should show you if DOS
is really trying to communicate with your terminal.

3. I still can't find my manual for the Horizon that shows how to set
the DIP headers (the "plugs" are called DIP headers). Here a RS-232
break-out box would be handy. If you don't have one, I would try
setting the Horizon to 300 baud (with that switch in the back) and
your terminal to 9600 baud. That should give you a couple of lines
of garbage if any thing comes across the line. Remember to set your
terminal to 8 bits, no parity, 1 stop bit, no flow control, and if
you are using your PC as a terminal which would be best, emulate
just a standard ANSI-BBS terminal. When I use my PC as a terminal,
I use a straight through 25 wire ribbon cable, but try your Null
Modem cable too.
 If you get the garbage then set your terminal to the same speed

as the Horizon. And remember that the Horizon may not boot when
powered on, you may have to hit the reset switch in the back.

 Let me know what you find.
And I'll send the games to you next week (have to work this
weekend).

 
=========================================
Doug Coward
Press Start Inc.
Sunnyvale,CA
=========================================
Received on Fri Oct 09 1998 - 15:43:38 BST