NorthStar Advantage Computer

THIS DOCUMENT IS A WORK-IN-PROGRESS

The NorthStar Advantage, shortened to Advantage throughout this page, is a z80-based business focussed all-in-one microcomputer designed and sold by NorthStar Computer Systems, Inc. circa 1981.

Computer Specs

Dimensions 48 cm wide x 51 cm long x 31.5 cm high
Net Weight 19.5 kg (43 lbs)
CPU Z80 Microprocessor, operating speed: 4MHz
8035 auxiliary processor for keyboard and disk
Memory 64K byte Main RAM
20K byte Display RAM
2K byte Boot PROM
Screen 28 cm (11 in) diagonal
P31 phosphor (green)
Grid 1920 character display,
24 lines by 80 characters
5x7 character in 8x10 dot matrix
Graphics resolution 240 pixels high x 640 pixels wide
Refresh rate 50 or 60 Hz, depending on line frequency
Keyboard 87 Keys, N-Key roll-over for fast data entry (w/ 7-key buffer)
Number of drives Two floppy disk drives (OR One and a Harddisk)
Diskettes Standard 5-1/4 in floppy diskettes. Recomended type: Dysan part No. 107/2D.
512 bytes/sector, 10 (hard) sectors/track, 35 tracks/side, 2 sides/diskette
Storage 360K bytes for DSDD, 175K bytes for SSDD (formatted)
Disk Speed 300 rpm ± 3.0%
I/O Bus Slots for up to six(6) plug-in boards, Each board addressed by 16 I/O addresses
Serioal I/O (SIO) RS232 Seerial Port, DB25
Current loop option
Asynchronous: 45 baud to 19.2 kilobaud
Synchonous: 2400 baud to 51 kilobaud
Parallel I/O (PIO) 8-bit data in and out with three handshake lines for each port
Maximum speed is limited by the processor.

Operating Systems

this list is non-exaustive.

Official Documentation

this list is non-exaustive.

Some information listed in the manuals is incorrect, please refer to the Unofficial Documentation section for manual corrections and for more undocumented features.

Disk Archives

Unofficial Documentation

Initial State (Pre-PROM)

Keyboard MI Flag Command

This command, command 3, returns the previous state of the register in bit 0 of status reg 2. The manual implies that it should return the newly complimented value, but their DOS expects otherwise.

Track Step Counting

The track counts on side 0 from inner to outer, 0-34, and on side 1 from outer to inner, 35-69. Either side is incremented in inverse direction to the other.

Show Sector Command

Something to keep in mind. The "Show Sector" command (control reg command 0) returns the previous sector's number. So to know we are at sector 2 we wait until we read sector 1 from the command.

Okay. The floppy disks are hard sectored. they have 10 hard sectors, but they have 11 holes because sector 0 has two punchouts to easier detect the start. The second punchout generates the index pulse.

When the index pulse is detected it returns 0xf instead of, as you would expect, 9. (since it returns the previous when we are at sector 0, it returns 9's sector which gets replaced by 0xf given the index).

Sector Number Order: 0 1 2 3 4 5 6 7 8 F

Floppy Sync2 Calculation

The formula listed on page 3-35 of the Technical manual does not match the sync2 calculation used by Northstar's CP/M or GDOS BIOSs.

Please note that this byte is checked in software, NOT hardware. As such, the formula may differ between different OSs. But that the "Corrected" formula IS what was used in Northstar's official Code.

formulas are assuming all operators have equal priority, read/exec left to right.

both formulas expect to take a side, track, and sector as inputs. In the case of Corrected Sync2, right_rotate is a wrapping >>.

Incorrect Sync2 (sector + (16 * track)) & 0xff
Corrected Sync2 (((track | (side << 6)) right_rotate 2) & 0x0f | sector
Optimized Sync2 ((track & 0x03) << 6) | (side << 4) | sector

Additional Resources