kair.us/ projects/ hardsid_isa/

Hardsid ISA clone

This is a reincarnation of the Hardsid clone which I made almost 20 years ago. The back story on that page is true, me and my colleague really had intention to make a PCI version which would be software compatible with the Hardsid ISA. We had working code for PCI interface implemented with Altera FPGA from another project. It didn't really support all the PCI features, but it realized a few I/O addresses for read and write operations. When the official Hardsid PCI was released, we kind of lost the interest, even though it would have been a fun project.

I didn't receive any emails about the Hardsid clone schematics and layout files until the last two years. I have had a few requests if I still have the Gerber files available. Sure enough, I still had the Eagle design available. Instead of just providing the Gerbers, I have made some slight changes to the layout as well. My original design was nearly 100% clone of the original Hardsid ISA. But it was difficult to source the ISA bracket for that. I used one from ISA network card but it wasn't really a good fit. There are still ISA brackets commercially available, and I chose to use the Keystone 9202, which is available from several distributors. It was necessary to increase the board size a little, to accommodate the 9202 screw locations. I also swapped the EXT In and RCA out connector locations in order to make room for the second screw hole. These changes also make the board look different enough compared to original Harsid ISA, hopefully preventing anyone selling this clone as original. Below is Eagle3D / POV-Ray render of the 'new' clone board.

Hardsid ISA clone rendered with
      Eagle3D / POV-Ray

And here are downloads for the design files, Gerber files and BOM. You can order bare boards from PCBWay using this link. And here is Mouser shared project which contains all the components for the project (except the SID!)

hardsid_isa.zip                                Eagle .sch and .brd
hardsid_isa_gerbers.zip                  Gerber files
hardsid_isa_circuit_diagram.pdf    Circuit diagram
hardsid_isa_assy_dwg.pdf              Assembly drawing
hardsid_isa_bom.xls                        Bill of materials, exported from the Mouser project

About component selection

Although the circuit diagram and assembly drawing indicate HC logic family, I have selected HCT family parts for the Mouser project BOM. This is because the ISA bus was originally specified for TTL, not CMOS logic levels. I have used HC chips in my build, and the board has been working flawlessly with several motherboards. They have all been quite late models from late 90's or early 2000, so maybe those have CMOS levels on the ISA bus also. I think the original Hardsid ISA used LS family, but I can't be sure because I didn't check the voltage levels. The markings on the chips were sanded off and painted black. LS chip availability seems to get worse nowadays, especially the 74LS574 is difficult to get now. So my recommendation is HCT, but the HC and LS should work as well. Just don't use a mix of HC and LS chips, it will cause problems!

Note that I haven't ordered the complete Mouser project BOM myself, so I can't be sure that all components are correct. If you build this board with components from the Mouser shared project, let me know about the results!

Photo

Finally, here's a group photo of the original clone and the new clone. And there's also my Catweasel Mk3 PCI board as bonus. The Catweasel is mainly intended as a versatile floppy interface, but it includes a socket for SID also. The SID implementation on the Catweasel is a little weird. It has a circuit to boost the 'digi-sound' on the MOS8580. But the filter capacitors are not easily changeable, and their capacitance is chosen to fit the MOS6581!

Hardsid ISA
      and Catweasel MK3 PCI / Zorro flipper interface

kair.us/ projects/ hardsid_isa/

page created 10.9.2020
last updated 26.10.2020 webmaster@kair.us