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deramp5113
October 31st, 2015, 04:41 PM
I recently started work on restoration of a North Star Horizon purchased off eBay early this year. The first thing I learned about the Horizon computer is that a ROM monitor is not typically part of the system. This, of course, means there is no way to isolate and test the CPU board, the RAM boards, the logic on the motherboard, or the floppy drives, short of most all of that already working properly and having a working boot disk of CP/M, North Star DOS, etc.

The North Star ZPB-A CPU board provided with the Horizon has a "PROM option" that allows installation of 2708 EPROM. This requires two regulators to generate +12v and -5v for the 2708, a couple of 74LS136's for address decoding, and the 2708 itself. I could install these parts, but I still needed to find/write a monitor for the Horizon.

I have a number of Vector Graphic systems and their "Extended Systems Monitor" was a great candidate for using on the Horizon. It is a full featured monitor, including the modern-day addition of an Intel hex loader. The monitor already uses the same 8251 UARTs and I/O addresses as used in the Horizon, so the port to the Horizon is very simple.

The only problem with using the VG monitor in the Horizon is that the VG monitor requires a 2716 or larger. After a quick look at the schematics for the ZPB-A CPU, it became clear that supporting a 2716 or 2732 on the CPU board was actually simpler than installing the "normal" PROM option for the 2708 since the two additional voltage regulators are not required.

I have posted the Vector Graphic monitor ported to the Horizon, along with notes about using a 2716/2732 on the ZPB-A board at http://deramp.com/downloads/index.php?dir=north_star%2Fhorizon%2Froms%2F.

With the monitor in place, and the ability to load hex files, I was able to debug and repair the memory boards and disk drives. I created PC2Flop and Flop2PC disk image utilities for writing and reading disk images over a serial port. These utilities, along with a few CP/M and North Star DOS disk images are available at http://deramp.com/downloads/index.php?dir=north_star%2Fhorizon%2F. These utilities use the same .NSI image format as Dave Dunfield's NST utilities, however, they're a bit more straight-forward to use.

My Horizon is now 100% functional with aligned floppy drives, an integral Virtual Sector Generator (so I can interchangeably use hard sector or soft sectored media), and a full featured monitor. Since the computer now powers on to the monitor, and booting a floppy is as simple as a single character "B"oot command, I no longer have to insert a floppy and then apply power - that made me really nervous with these old machines :)

Mike

deramp5113
February 7th, 2018, 07:29 PM
I recently started work on restoration of a North Star Horizon purchased off eBay early this year. The first thing I learned about the Horizon computer is that a ROM monitor is not typically part of the system. This, of course, means there is no way to isolate and test the CPU board, the RAM boards, the logic on the motherboard, or the floppy drives, short of most all of that already working properly and having a working boot disk of CP/M, North Star DOS, etc.

The North Star ZPB-A CPU board provided with the Horizon has a "PROM option" that allows installation of 2708 EPROM. This requires two regulators to generate +12v and -5v for the 2708, a couple of 74LS136's for address decoding, and the 2708 itself. I could install these parts, but I still needed to find/write a monitor for the Horizon.

I have a number of Vector Graphic systems and their "Extended Systems Monitor" was a great candidate for using on the Horizon. It is a full featured monitor, including the modern-day addition of an Intel hex loader. The monitor already uses the same 8251 UARTs and I/O addresses as used in the Horizon, so the port to the Horizon is very simple.

The only problem with using the VG monitor in the Horizon is that the VG monitor requires a 2716 or larger. After a quick look at the schematics for the ZPB-A CPU, it became clear that supporting a 2716 or 2732 on the CPU board was actually simpler than installing the "normal" PROM option for the 2708 since the two additional voltage regulators are not required.

I have posted the Vector Graphic monitor ported to the Horizon, along with notes about using a 2716/2732 on the ZPB-A board at http://deramp.com/downloads/index.php?dir=north_star%2Fhorizon%2Froms%2F.

With the monitor in place, and the ability to load hex files, I was able to debug and repair the memory boards and disk drives. I created PC2Flop and Flop2PC disk image utilities for writing and reading disk images over a serial port. These utilities, along with a few CP/M and North Star DOS disk images are available at http://deramp.com/downloads/index.php?dir=north_star%2Fhorizon%2F. These utilities use the same .NSI image format as Dave Dunfield's NST utilities, however, they're a bit more straight-forward to use.

My Horizon is now 100% functional with aligned floppy drives, an integral Virtual Sector Generator (so I can interchangeably use hard sector or soft sectored media), and a full featured monitor. Since the computer now powers on to the monitor, and booting a floppy is as simple as a single character "B"oot command, I no longer have to insert a floppy and then apply power - that made me really nervous with these old machines :)

Mike

Updated links for the above information:

I have posted the Vector Graphic monitor ported to the Horizon, along with notes about using a 2716/2732 on the ZPB-A board at http://deramp.com/downloads/north_star/horizon/roms/.

With the monitor in place, and the ability to load hex files, I was able to debug and repair the memory boards and disk drives. I created PC2Flop and Flop2PC disk image utilities for writing and reading disk images over a serial port. These utilities, along with a few CP/M and North Star DOS disk images are available at http://deramp.com/downloads/north_star/horizon/. These utilities use the same .NSI image format as Dave Dunfield's NST utilities, however, they're a bit more straight-forward to use.

jaquinn
February 9th, 2018, 04:00 PM
Updated links for the above information:

I have posted the Vector Graphic monitor ported to the Horizon, along with notes about using a 2716/2732 on the ZPB-A board at http://deramp.com/downloads/north_star/horizon/roms/.

Thanks for this. I have a couple of ZPB-A boards to test and it will be a great help.