S100 Computers

Home S-100 Boards History New Boards Software Boards For Sale
Forum Other Web Sites News Index    
NorthStar - MDS
This "MDS  board"  was a double density later version of the original NorthStar's Micro-Disk System disk controller, the MDC.

Northstar MDS FDC Board

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.
The manual for this board can be obtained here


Other NorthStar S-100 Boards
16K Dynamic RAM     32K Dynamic RAM    48K Dynamic RAM    64K Dynamic RAM    8088-SBC  
FP Board   MDC-FDC   MDS-FDC   SIO   UP8   Z80CPU  HDC



This page was last modified on 10/25/2013