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.
This effectively maps the 16 bytes of IO memory on the CS8900a making it accessible to the 6510 CPU at $DE00-$DEFF (obviously $DE00-$DE0F is mirrored into $DE10-$DE1F, $DE30-$DE3F etc).
Amund Gjerde Gjendem's revised TFE layouts with extra jumpers makes it possible to choose the I/O memory area (i.e., $DE00-$DE0F, $DE10-$DE1F, $DE40-$DE4F, or $DE50-$DE5F). The layouts are avaliable here (in PDF format): side 1, side 2, the silk layer. Many thanks for his work!
BEWARE this layout is currently FAULTY. The read and write signals for the Embedded ethernet board were switched. Several hours of debugging and some external wires were spent because of this silly mistake. (As can be seen on the pictures.)
Our original schematics show how it should have been done (and is currently not reflected by our faulty layout).
$Date: 2002/10/17 19:25:07 $