NorthStar - MDS This "MDS board" was a double density later version of the
original NorthStar's Micro-Disk System disk controller, the
MDC.
As for their earlier controller(s), commands to the disk controller
were
specified by memory read references to addresses within a particular 1K byte
block of the CPU address space. The default location was E800H. Bootstrap software (in 8080/Z80 machine
code) was stored in the on-board 256 byte custom bipolar PROM (DPGM, 9D). This
PROM provides 256 bytes of memory. The 8 low order address bits address the
proms. The PROM outputs are driven onto the Data Input Bus.
Raw data from the disk was standardized
by the RD-DAT-OS one-shot (5A). A phase-locked loop (1A, 4A, and parts of 1B,
5A) tracks the trailing edge of RD-DAT-OS to match the frequency of the incoming
data (see manual below). The phase-locked loop output drives the data separator (3B, 4D), whose
outputs, DATA-WINDOW (clock) and WIND-DATA (data), go to the 8-bit read data
shift register (15D). The read shift register outputs are multiplexed with the
status bits (12D, 13D, 14D) and driven onto the Data Input Bus (100, 11D). When
reading, if double density data is encountered, the double density indicator
(DDI, 4B) was set.
Disks had 35 tracks of data in 10
sectors per track. Sectors were 256 Bytes/sector is single density and 512
bytes/sector in double density.
While the standard software supplied
was not interrupt driven the board could be configured to trigger interrupts.
