Yesterday evening I was able to correct the problems with the pulse generator of my datassette emulator. The first problem was incompatibility between signal levels that I corrected by adding a 4k7 pull-up resistor to the "cassette read" signal. The second problem was in the programming. Even though I had read somewhere that the signal polarity is significant, I thought that it is nonsense, since the C64 only monitors high-to-low transitions on the signal. I was surprised when the VIC-20 finally recognized the pulse stream, after I modified the firmware so that the cassette read line is at low voltage level when inactive. The only difference from the previous firmware was the polarity inversion. I could now upload the schematic diagram and the board layout to FUNET, but I can't right now, since the server seems to be out of service. Until the documents are available there, interested parties can request the files from me by e-mail. The circuit board is simple; there are no jumper wires. Therefore I suggest that those who are interested in the device build it themselves. A summary of the features: - few components: five capacitors, three resistors and two ICs, plus connectors - standard RS-232 connection with hardware handshaking (CTS/RTS) (could be easily changed to software handhshaking (XON/XOFF)) - supports tape loading and saving (no feedback from the cassette motor signal) - supports a custom transfer protocol similar to prlink (coming soon) - could be used to interface a Commodore serial bus disk drive or printer emulator that runs on the other end of the RS-232 line (I'm not going to implement this) Marko Message was sent through the cbm-hackers mailing list
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