Board
Photo (JPG 66K)Board Photo High Resolution (JPG 256K)
The DC5 Floppy Disk Controller is an all-new design for the Southwest Technical Products Corp. 6800 and 6809 computers. It plugs into the SS-30 I/O bus and fully emulates the SWTPC DC4 controller and clones. It supports double-sided, double-density disk for both 5.25-inch and 3.5-inch floppy drives. The DC5 will boot and run all SWTPC Disk Operating Systems (that were designed for the DC1 to DC4 controllers). The board will fit into the original SWTPC 6800 case or the later cases that had openings in the back like the S/09.
This new design uses a WD2797 that is a super set of the WD1797 and WD1691 chips that were used on the DC4. The earlier SWTPC controllers (DC1, DC2 and DC3) used the Western Digital FD1771 FDC chip that only supported single-density disks. The board was designed so that FD1771 chips could be used with a few cuts and jumpers.
A Programmable Logic Device was used to reduce chip count and make the printed circuit board, PCB, layout easier. A Xilinx XC9572 CPLD was chosen because the development tools are free, the chip is low cost and it is easily programmed in circuit. The design only uses about half of the XC9572 resources so additional features can be added in the future.
More information about SWTPC computers can be found here. The FLEX User's Group has documention on the FLEX disk operating system for the 6800 amd 6809.
DC5 Users Guide Rev 2a (PDF 239K) (Revised April 29, 2003)
Schematic single page 11 x 17 (PDF 113K) (Revised March 20, 2003)
Schematic 3 pages 8.5 x 11 (PDF 154K) (Revised March 20, 2003)
Printed Circuit Board layout (PDF 83K)
TMS2797 / WD2797 Data Sheet (PDF 335K).
The control logic has been compressed into a single Programmable Logic Device. A Xilinx 9572 CPLD was chosen because the development tools are free and it is easily programmed in circuit. The chip is available from Digi-Key for about $6. The CPLD was used to reduce chip count and make the printed circuit board layout easier.
This revision was done in Verilog using Xilinx WebPACK 4.1 software.
DC5 CPLD Functional Block Diagram (PDF 10K)
DC5 Design Description (PDF 419K)
Verilog Logic Design - (ZIP 36K)
