Ethernet board for C64 and SX-64

  
Once i had my SX-64 repaired i wanted to do something cool with it. I learned about people who added ethernet interfaces to their C64 and since i had some spare ones of the required ethernet chips, i decided to build the net64 cartridge. See the image above for my SX-64 with the net64 cartridge installed. The net64 cartridge is compatible to the final ethernet cartridge and can be operated with software developed for the tfe.
Ethernet board for C64 and SX-64 - schematic

The TFE adapter plugs into the cartridge expansion port on the back of the Commodore 64. It does not require any extra hardware. The TFE consists of one CS8900a based Embedded Ethernet board and some simple glue logic for interfacing with the C64. The glue logic and the Embedded ethernet board is mounted on a custom created PCB for which the schematics can be seen below. The schematics and the layout were made using Orcad and the PCB was created at the ELAB electronics society of the Royal Institute of Technology in Stockholm. Many thanks for their help! The C64 8-bit data bus and the low 4 bits of its address bus are directly connected to their equivalents on the CS8900a ISA bus. The IO/1 and the R/W signal from the C64 are used to create the ISA control signals using the 74LS139 decoder. The ISA signal address enable is always active (tied low) and IO/1 is connected to the gate of the decoder.



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