NorthStar - MDC
This was the board that essentially
launched NorthStar. It provided the hobbyist a simple reasonable way to access
the then new 5" floppy disk drives.
NorthStar sold this board as a package
along with a Shugart SA-400 mini-floppy disk drive. The disks were hard-sectored
256-byte sectors, each diskette could store 89.6K bytes of information,
formatted as 35 tracks with 10 sectors per track in single density.
Track-to-track access was 40ms and latency was 100ms. The data transfer rate was
125K bits per second. The drive of course comes assembled and tested.
The controller was a single PC board
that plugs directly into the S-100 bus. Commands and data were transferred under
software control by the technique of memory-mapped I/O (no I/O ports or DMA were
used). Up to three drives could be controlled, with or without interrupts. The
controller allows transfer of between one and ten 256-byte blocks of data
between the diskette and RAM in a single revolution. CRC error checking was done
for each block read from disk. The controller automatically turned the drives on
and off to minimize head and diskette wear. The controller consists of LS and S
7400 chips and included its own crystal-controlled clock.
The NorthStar Disk Operating System and
extended disk BASIC were included on diskette with the MICRO-DISK SYSTEM. A
comprehensive monitor program for hardware and software maintenance was also
provided on diskette.
The controller included an on-board
PROM, pre-programmed to permit power-on start-up of the computer. The PROM
program loaded the DOS from drive number 1 into memory and then branches to the
loaded DOS. Much of the low-level software for the DOS was contained on he
PROM. The on-board PROM and the memory-mapped I/O together used 1K of the
computer address space, starting at E800H in the standard NorthStar version.
There appears to have been 3 version of this board. MDC-A1, MDC-A1 and MDC-A4.
I'm not sure what the difference is. Also the manual refers to the "system" as
the MDS of Micro-Disk System. The later boards were actually called the MDS-AD2
or MDS-AD3. I'm therefore not sure which manuals actually correspond to
this board but try this one here.
NorthStar's Basic interpreter was quite
good and for a small hardware house they did a good job with software support.
An overview of the NorthStar DOS and
Basic software can be seen
Other NorthStar S-100 Boards
16K Dynamic RAM
32K Dynamic RAM
48K Dynamic RAM
64K Dynamic RAM
FP Board MDC-FDC
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